--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -1293,16 +1293,17 @@ pref("services.sync.prefs.sync.privacy.c
 pref("services.sync.prefs.sync.privacy.clearOnShutdown.formdata", true);
 pref("services.sync.prefs.sync.privacy.clearOnShutdown.history", true);
 pref("services.sync.prefs.sync.privacy.clearOnShutdown.offlineApps", true);
 pref("services.sync.prefs.sync.privacy.clearOnShutdown.sessions", true);
 pref("services.sync.prefs.sync.privacy.clearOnShutdown.siteSettings", true);
 pref("services.sync.prefs.sync.privacy.donottrackheader.enabled", true);
 pref("services.sync.prefs.sync.privacy.sanitize.sanitizeOnShutdown", true);
 pref("services.sync.prefs.sync.privacy.trackingprotection.enabled", true);
+pref("services.sync.prefs.sync.privacy.trackingprotection.pbmode.enabled", true);
 pref("services.sync.prefs.sync.security.OCSP.enabled", true);
 pref("services.sync.prefs.sync.security.OCSP.require", true);
 pref("services.sync.prefs.sync.security.default_personal_cert", true);
 pref("services.sync.prefs.sync.security.tls.version.min", true);
 pref("services.sync.prefs.sync.security.tls.version.max", true);
 pref("services.sync.prefs.sync.signon.rememberSignons", true);
 pref("services.sync.prefs.sync.spellchecker.dictionary", true);
 pref("services.sync.prefs.sync.xpinstall.whitelist.required", true);

--- a/build/gen_test_packages_manifest.py
+++ b/build/gen_test_packages_manifest.py
@@ -13,24 +13,26 @@ ALL_HARNESSES = [
     'mochitest',
     'reftest',
     'webapprt',
     'xpcshell',
     'cppunittest',
     'jittest',
     'mozbase',
     'web-platform',
+    'talos',
 ]
 
 PACKAGE_SPECIFIED_HARNESSES = [
     'cppunittest',
     'mochitest',
     'reftest',
     'xpcshell',
     'web-platform',
+    'talos',
 ]
 
 
 def parse_args():
     parser = ArgumentParser(description='Generate a test_packages.json file to tell automation which harnesses require which test packages.')
     parser.add_argument("--common", required=True,
                         action="store", dest="tests_common",
                         help="Name of the \"common\" archive, a package to be used by all harnesses.")

--- a/build/unix/stdc++compat/Makefile.in
+++ b/build/unix/stdc++compat/Makefile.in
@@ -1,10 +1,7 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this file,
 # You can obtain one at http://mozilla.org/MPL/2.0/.
 
 ENABLE_CLANG_PLUGIN :=
 
 include $(topsrcdir)/config/rules.mk
-
-CXXFLAGS += -DMOZ_LIBSTDCXX_VERSION=$(MOZ_LIBSTDCXX_TARGET_VERSION)
-HOST_CXXFLAGS += -DMOZ_LIBSTDCXX_VERSION=$(MOZ_LIBSTDCXX_HOST_VERSION)

--- a/build/unix/stdc++compat/moz.build
+++ b/build/unix/stdc++compat/moz.build
@@ -14,8 +14,11 @@ if CONFIG['MOZ_LIBSTDCXX_HOST_VERSION']:
         'stdc++compat.cpp',
     ]
 
 FORCE_STATIC_LIB = True
 
 NO_PGO = True
 
 DISABLE_STL_WRAPPING = True
+
+DEFINES['MOZ_LIBSTDCXX_VERSION'] = CONFIG['MOZ_LIBSTDCXX_TARGET_VERSION']
+HOST_DEFINES['MOZ_LIBSTDCXX_VERSION'] = CONFIG['MOZ_LIBSTDCXX_HOST_VERSION']

--- a/config/Makefile.in
+++ b/config/Makefile.in
@@ -36,18 +36,16 @@ HEADERS_FILES = \
 	$(NULL)
 HEADERS_DEST := $(DIST)/include
 HEADERS_TARGET := export
 INSTALL_TARGETS += HEADERS
 endif
 
 include $(topsrcdir)/config/rules.mk
 
-HOST_CFLAGS += -DUNICODE -D_UNICODE
-
 ifndef JS_STANDALONE
 ifndef MOZ_PROFILE_USE
 # Generate a new buildid every time we "export" in config... that's only
 # supposed to be once per-build!
 export::
 ifdef MOZ_BUILD_DATE
 	printf '%s' $(MOZ_BUILD_DATE) > buildid
 else

--- a/config/config.mk
+++ b/config/config.mk
@@ -423,16 +423,19 @@ COMPILE_CXXFLAGS = $(if $(DISABLE_STL_WR
 COMPILE_CMFLAGS = $(OS_COMPILE_CMFLAGS) $(MOZBUILD_CMFLAGS)
 COMPILE_CMMFLAGS = $(OS_COMPILE_CMMFLAGS) $(MOZBUILD_CMMFLAGS)
 ASFLAGS += $(MOZBUILD_ASFLAGS)
 
 ifndef CROSS_COMPILE
 HOST_CFLAGS += $(RTL_FLAGS)
 endif
 
+HOST_CFLAGS += $(HOST_DEFINES) $(MOZBUILD_HOST_CFLAGS)
+HOST_CXXFLAGS += $(HOST_DEFINES) $(MOZBUILD_HOST_CXXFLAGS)
+
 #
 # Name of the binary code directories
 #
 # Override defaults
 
 # Default location of include files
 ifndef LIBXUL_SDK
 IDL_PARSER_DIR = $(topsrcdir)/xpcom/idl-parser

--- a/config/moz.build
+++ b/config/moz.build
@@ -40,8 +40,13 @@ PYTHON_UNIT_TESTS += [
     'tests/unit-printprereleasesuffix.py',
 ]
 
 if CONFIG['GNU_CC'] and CONFIG['MOZ_OPTIMIZE']:
     CFLAGS += ['-O3']
 
 # XXX: We should fix these warnings.
 ALLOW_COMPILER_WARNINGS = True
+
+HOST_DEFINES = {
+    'UNICODE': True,
+    '_UNICODE': True,
+}

--- a/configure.in
+++ b/configure.in
@@ -1478,17 +1478,16 @@ if test "$GNU_CC"; then
     fi
 
     # Turn on gcc/clang warnings:
     # https://gcc.gnu.org/onlinedocs/gcc-4.4.0/gcc/Warning-Options.html
     #
     # -Wall - turn on a lot of warnings
     # -Wchar-subscripts - catches array index using signed char
     # -Wcomment - catches nested comments
-    # -Wdeclaration-after-statement - MSVC doesn't like these
     # -Wempty-body - catches bugs, e.g. "if (c); foo();", few false positives
     # -Wendif-labels - catches `#else FOO` and `#endif FOO` not in comment
     # -Wenum-compare - catches comparison of different enum types
     # -Wignored-qualifiers - catches returns types with qualifiers like const
     # -Wint-to-pointer-cast - catches cast to pointer from integer of different size
     # -Wmultichar - catches multicharacter integer constants like 'THIS'
     # -Wnon-literal-null-conversion - catches expressions used as a null pointer constant
     # -Wnonnull - catches NULL used with functions arguments marked as non-null
@@ -1498,17 +1497,16 @@ if test "$GNU_CC"; then
     # -Wreturn-type - catches missing returns, zero false positives
     # -Wsequence-point - catches undefined order behavior like `a = a++`
     # -Wsign-compare - catches comparison of signed and unsigned types
     # -Wtrigraphs - catches unlikely use of trigraphs
     # -Wtype-limits - catches overflow bugs, few false positives
     # -Wunknown-pragmas - catches unexpected #pragma directives
     #
     _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wall"
-    _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wdeclaration-after-statement"
     _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wempty-body"
     _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wpointer-to-int-cast"
     _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wsign-compare"
     _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Wtype-limits"
 
     # Treat some warnings as errors if --enable-warnings-as-errors:
     if test "$MOZ_ENABLE_WARNINGS_AS_ERRORS"; then
         _WARNINGS_CFLAGS="${_WARNINGS_CFLAGS} -Werror=char-subscripts"
@@ -1834,17 +1832,17 @@ case "$host" in
         HOST_AR=lib
         HOST_AR_FLAGS='-NOLOGO -OUT:$@'
         HOST_CFLAGS="$HOST_CFLAGS -TC -nologo"
         HOST_RANLIB='echo ranlib'
     else
         HOST_CFLAGS="$HOST_CFLAGS -mwindows"
     fi
     HOST_CFLAGS="$HOST_CFLAGS -DXP_WIN32 -DXP_WIN -DWIN32 -D_WIN32 -DNO_X11 -D_CRT_SECURE_NO_WARNINGS"
-    HOST_NSPR_MDCPUCFG='\"md/_winnt.cfg\"'
+    HOST_NSPR_MDCPUCFG='"md/_winnt.cfg"'
     HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O2}"
     HOST_BIN_SUFFIX=.exe
     case "$host" in
     *mingw*)
         PERL="/bin/sh ${_topsrcdir}/build/msys-perl-wrapper"
         ;;
     esac
 
@@ -1860,23 +1858,23 @@ case "$host" in
         fi
         HOST_CFLAGS="$HOST_CFLAGS -D_AMD64_"
         ;;
     esac
     ;;
 
 *-darwin*)
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX -DXP_MACOSX -DNO_X11"
-    HOST_NSPR_MDCPUCFG='\"md/_darwin.cfg\"'
+    HOST_NSPR_MDCPUCFG='"md/_darwin.cfg"'
     HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O3}"
     ;;
 
 *-linux*|*-kfreebsd*-gnu|*-gnu*)
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX"
-    HOST_NSPR_MDCPUCFG='\"md/_linux.cfg\"'
+    HOST_NSPR_MDCPUCFG='"md/_linux.cfg"'
     HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O3}"
     ;;
 
 *)
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX"
     HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O2}"
     ;;
 esac

--- a/dom/base/File.cpp
+++ b/dom/base/File.cpp
@@ -375,28 +375,16 @@ Blob::Constructor(
 }
 
 int64_t
 Blob::GetFileId()
 {
   return mImpl->GetFileId();
 }
 
-void
-Blob::AddFileInfo(indexedDB::FileInfo* aFileInfo)
-{
-  mImpl->AddFileInfo(aFileInfo);
-}
-
-indexedDB::FileInfo*
-Blob::GetFileInfo(indexedDB::FileManager* aFileManager)
-{
-  return mImpl->GetFileInfo(aFileManager);
-}
-
 bool
 Blob::IsMemoryFile() const
 {
   return mImpl->IsMemoryFile();
 }
 
 void
 Blob::GetInternalStream(nsIInputStream** aStream, ErrorResult& aRv)
@@ -457,46 +445,16 @@ File::CreateMemoryFile(nsISupports* aPar
 /* static */ already_AddRefed<File>
 File::CreateFromFile(nsISupports* aParent, nsIFile* aFile, bool aTemporary)
 {
   nsRefPtr<File> file = new File(aParent, new BlobImplFile(aFile, aTemporary));
   return file.forget();
 }
 
 /* static */ already_AddRefed<File>
-File::CreateFromFile(nsISupports* aParent, const nsAString& aContentType,
-                     uint64_t aLength, nsIFile* aFile,
-                     indexedDB::FileInfo* aFileInfo)
-{
-  nsRefPtr<File> file = new File(aParent,
-    new BlobImplFile(aContentType, aLength, aFile, aFileInfo));
-  return file.forget();
-}
-
-/* static */ already_AddRefed<File>
-File::CreateFromFile(nsISupports* aParent, const nsAString& aName,
-                     const nsAString& aContentType,
-                     uint64_t aLength, nsIFile* aFile,
-                     indexedDB::FileInfo* aFileInfo)
-{
-  nsRefPtr<File> file = new File(aParent,
-    new BlobImplFile(aName, aContentType, aLength, aFile, aFileInfo));
-  return file.forget();
-}
-
-/* static */ already_AddRefed<File>
-File::CreateFromFile(nsISupports* aParent, nsIFile* aFile,
-                     indexedDB::FileInfo* aFileInfo)
-{
-  nsRefPtr<File> file = new File(aParent,
-    new BlobImplFile(aFile, aFileInfo));
-  return file.forget();
-}
-
-/* static */ already_AddRefed<File>
 File::CreateFromFile(nsISupports* aParent, nsIFile* aFile,
                      const nsAString& aName, const nsAString& aContentType)
 {
   nsRefPtr<File> file = new File(aParent,
     new BlobImplFile(aFile, aName, aContentType));
   return file.forget();
 }
 
@@ -795,88 +753,17 @@ void
 BlobImplBase::SetLastModified(int64_t aLastModified)
 {
   mLastModificationDate = aLastModified * PR_USEC_PER_MSEC;
 }
 
 int64_t
 BlobImplBase::GetFileId()
 {
-  int64_t id = -1;
-
-  if (IsStoredFile() && IsWholeFile() && !IsSnapshot()) {
-    if (!indexedDB::IndexedDatabaseManager::IsClosed()) {
-      indexedDB::IndexedDatabaseManager::FileMutex().Lock();
-    }
-
-    NS_ASSERTION(!mFileInfos.IsEmpty(),
-                 "A stored file must have at least one file info!");
-
-    nsRefPtr<indexedDB::FileInfo>& fileInfo = mFileInfos.ElementAt(0);
-    if (fileInfo) {
-      id =  fileInfo->Id();
-    }
-
-    if (!indexedDB::IndexedDatabaseManager::IsClosed()) {
-      indexedDB::IndexedDatabaseManager::FileMutex().Unlock();
-    }
-  }
-
-  return id;
-}
-
-void
-BlobImplBase::AddFileInfo(indexedDB::FileInfo* aFileInfo)
-{
-  if (indexedDB::IndexedDatabaseManager::IsClosed()) {
-    NS_ERROR("Shouldn't be called after shutdown!");
-    return;
-  }
-
-  nsRefPtr<indexedDB::FileInfo> fileInfo = aFileInfo;
-
-  MutexAutoLock lock(indexedDB::IndexedDatabaseManager::FileMutex());
-
-  NS_ASSERTION(!mFileInfos.Contains(aFileInfo),
-               "Adding the same file info agan?!");
-
-  nsRefPtr<indexedDB::FileInfo>* element = mFileInfos.AppendElement();
-  element->swap(fileInfo);
-}
-
-indexedDB::FileInfo*
-BlobImplBase::GetFileInfo(indexedDB::FileManager* aFileManager)
-{
-  if (indexedDB::IndexedDatabaseManager::IsClosed()) {
-    NS_ERROR("Shouldn't be called after shutdown!");
-    return nullptr;
-  }
-
-  // A slice created from a stored file must keep the file info alive.
-  // However, we don't support sharing of slices yet, so the slice must be
-  // copied again. That's why we have to ignore the first file info.
-  // Snapshots are handled in a similar way (they have to be copied).
-  uint32_t startIndex;
-  if (IsStoredFile() && (!IsWholeFile() || IsSnapshot())) {
-    startIndex = 1;
-  }
-  else {
-    startIndex = 0;
-  }
-
-  MutexAutoLock lock(indexedDB::IndexedDatabaseManager::FileMutex());
-
-  for (uint32_t i = startIndex; i < mFileInfos.Length(); i++) {
-    nsRefPtr<indexedDB::FileInfo>& fileInfo = mFileInfos.ElementAt(i);
-    if (fileInfo->Manager() == aFileManager) {
-      return fileInfo;
-    }
-  }
-
-  return nullptr;
+  return -1;
 }
 
 nsresult
 BlobImplBase::GetSendInfo(nsIInputStream** aBody, uint64_t* aContentLength,
                           nsACString& aContentType, nsACString& aCharset)
 {
   MOZ_ASSERT(aContentLength);
 

--- a/dom/base/File.h
+++ b/dom/base/File.h
@@ -3,25 +3,23 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef mozilla_dom_File_h
 #define mozilla_dom_File_h
 
 #include "mozilla/Attributes.h"
-
+#include "mozilla/ErrorResult.h"
 #include "mozilla/GuardObjects.h"
 #include "mozilla/LinkedList.h"
 #include "mozilla/StaticMutex.h"
 #include "mozilla/StaticPtr.h"
+#include "mozilla/dom/BindingDeclarations.h"
 #include "mozilla/dom/Date.h"
-#include "mozilla/dom/indexedDB/FileInfo.h"
-#include "mozilla/dom/indexedDB/FileManager.h"
-#include "mozilla/dom/indexedDB/IndexedDatabaseManager.h"
 #include "nsAutoPtr.h"
 #include "nsCycleCollectionParticipant.h"
 #include "nsCOMPtr.h"
 #include "nsIDOMBlob.h"
 #include "nsIFile.h"
 #include "nsIMutable.h"
 #include "nsIXMLHttpRequest.h"
 #include "nsString.h"
@@ -34,20 +32,16 @@ class nsIInputStream;
 
 #define BLOBIMPL_IID \
   { 0xbccb3275, 0x6778, 0x4ac5, \
     { 0xaf, 0x03, 0x90, 0xed, 0x37, 0xad, 0xdf, 0x5d } }
 
 namespace mozilla {
 namespace dom {
 
-namespace indexedDB {
-class FileInfo;
-} // namespace indexedDB
-
 struct BlobPropertyBag;
 struct ChromeFilePropertyBag;
 struct FilePropertyBag;
 class BlobImpl;
 class File;
 class OwningArrayBufferOrArrayBufferViewOrBlobOrString;
 
 /**
@@ -131,22 +125,16 @@ public:
               ErrorResult& aRv);
 
   void
   GetInternalStream(nsIInputStream** aStream, ErrorResult& aRv);
 
   int64_t
   GetFileId();
 
-  indexedDB::FileInfo*
-  GetFileInfo(indexedDB::FileManager* aFileManager);
-
-  void
-  AddFileInfo(indexedDB::FileInfo* aFileInfo);
-
   // WebIDL methods
   nsISupports* GetParentObject() const
   {
     return mParent;
   }
 
   bool
   IsMemoryFile() const;
@@ -217,30 +205,16 @@ public:
   CreateMemoryFile(nsISupports* aParent, void* aMemoryBuffer, uint64_t aLength,
                    const nsAString& aName, const nsAString& aContentType,
                    int64_t aLastModifiedDate);
 
   static already_AddRefed<File>
   CreateFromFile(nsISupports* aParent, nsIFile* aFile, bool aTemporary = false);
 
   static already_AddRefed<File>
-  CreateFromFile(nsISupports* aParent, const nsAString& aContentType,
-                 uint64_t aLength, nsIFile* aFile,
-                 indexedDB::FileInfo* aFileInfo);
-
-  static already_AddRefed<File>
-  CreateFromFile(nsISupports* aParent, const nsAString& aName,
-                 const nsAString& aContentType, uint64_t aLength,
-                 nsIFile* aFile, indexedDB::FileInfo* aFileInfo);
-
-  static already_AddRefed<File>
-  CreateFromFile(nsISupports* aParent, nsIFile* aFile,
-                 indexedDB::FileInfo* aFileInfo);
-
-  static already_AddRefed<File>
   CreateFromFile(nsISupports* aParent, nsIFile* aFile, const nsAString& aName,
                  const nsAString& aContentType);
 
   // WebIDL methods
 
   virtual JSObject* WrapObject(JSContext *cx,
                                JS::Handle<JSObject*> aGivenProto) override;
 
@@ -340,21 +314,16 @@ public:
   virtual const nsTArray<nsRefPtr<BlobImpl>>*
   GetSubBlobImpls() const = 0;
 
   virtual void GetInternalStream(nsIInputStream** aStream,
                                  ErrorResult& aRv) = 0;
 
   virtual int64_t GetFileId() = 0;
 
-  virtual void AddFileInfo(indexedDB::FileInfo* aFileInfo) = 0;
-
-  virtual indexedDB::FileInfo*
-  GetFileInfo(indexedDB::FileManager* aFileManager) = 0;
-
   virtual nsresult GetSendInfo(nsIInputStream** aBody,
                                uint64_t* aContentLength,
                                nsACString& aContentType,
                                nsACString& aCharset) = 0;
 
   virtual nsresult GetMutable(bool* aMutable) const = 0;
 
   virtual nsresult SetMutable(bool aMutable) = 0;
@@ -512,37 +481,30 @@ public:
   virtual void GetInternalStream(nsIInputStream** aStream,
                                  ErrorResult& aRv) override
   {
     aRv.Throw(NS_ERROR_NOT_IMPLEMENTED);
   }
 
   virtual int64_t GetFileId() override;
 
-  virtual void AddFileInfo(indexedDB::FileInfo* aFileInfo) override;
-
-  virtual indexedDB::FileInfo*
-  GetFileInfo(indexedDB::FileManager* aFileManager) override;
-
   virtual nsresult GetSendInfo(nsIInputStream** aBody,
                                uint64_t* aContentLength,
                                nsACString& aContentType,
                                nsACString& aCharset) override;
 
   virtual nsresult GetMutable(bool* aMutable) const override;
 
   virtual nsresult SetMutable(bool aMutable) override;
 
   virtual void
   SetLazyData(const nsAString& aName, const nsAString& aContentType,
               uint64_t aLength, int64_t aLastModifiedDate,
               BlobDirState aDirState) override
   {
-    NS_ASSERTION(aLength, "must have length");
-
     mName = aName;
     mContentType = aContentType;
     mLength = aLength;
     mLastModificationDate = aLastModifiedDate;
     mIsFile = !aName.IsVoid();
   }
 
   virtual bool IsMemoryFile() const override
@@ -585,72 +547,45 @@ public:
     return mDirState == BlobDirState::eIsDir;
   }
 
   virtual BlobDirState GetDirState() const override
   {
     return mDirState;
   }
 
-  virtual bool IsStoredFile() const
-  {
-    return false;
-  }
-
-  virtual bool IsWholeFile() const
-  {
-    NS_NOTREACHED("Should only be called on dom blobs backed by files!");
-    return false;
-  }
-
-  virtual bool IsSnapshot() const
-  {
-    return false;
-  }
-
   virtual bool IsSizeUnknown() const override
   {
     return mLength == UINT64_MAX;
   }
 
 protected:
   virtual ~BlobImplBase() {}
 
   /**
    * Returns a new, effectively-unique serial number. This should be used
    * by implementations to obtain a serial number for GetSerialNumber().
    * The implementation is thread safe.
    */
   static uint64_t NextSerialNumber();
 
-  indexedDB::FileInfo* GetFileInfo() const
-  {
-    NS_ASSERTION(IsStoredFile(), "Should only be called on stored files!");
-    NS_ASSERTION(!mFileInfos.IsEmpty(), "Must have at least one file info!");
-
-    return mFileInfos.ElementAt(0);
-  }
-
   bool mIsFile;
   bool mImmutable;
   BlobDirState mDirState;
 
   nsString mContentType;
   nsString mName;
   nsString mPath; // The path relative to a directory chosen by the user
 
   uint64_t mStart;
   uint64_t mLength;
 
   int64_t mLastModificationDate;
 
   const uint64_t mSerialNumber;
-
-  // Protected by IndexedDatabaseManager::FileMutex()
-  nsTArray<nsRefPtr<indexedDB::FileInfo>> mFileInfos;
 };
 
 /**
  * This class may be used off the main thread, and in particular, its
  * constructor and destructor may not run on the same thread.  Be careful!
  */
 class BlobImplMemory final : public BlobImplBase
 {
@@ -788,113 +723,65 @@ class BlobImplFile : public BlobImplBase
 public:
   NS_DECL_ISUPPORTS_INHERITED
 
   // Create as a file
   explicit BlobImplFile(nsIFile* aFile, bool aTemporary = false)
     : BlobImplBase(EmptyString(), EmptyString(), UINT64_MAX, INT64_MAX)
     , mFile(aFile)
     , mWholeFile(true)
-    , mStoredFile(false)
     , mIsTemporary(aTemporary)
   {
     NS_ASSERTION(mFile, "must have file");
     // Lazily get the content type and size
     mContentType.SetIsVoid(true);
     mFile->GetLeafName(mName);
   }
 
-  BlobImplFile(nsIFile* aFile, indexedDB::FileInfo* aFileInfo)
-    : BlobImplBase(EmptyString(), EmptyString(), UINT64_MAX, INT64_MAX)
-    , mFile(aFile)
-    , mWholeFile(true)
-    , mStoredFile(true)
-    , mIsTemporary(false)
-  {
-    NS_ASSERTION(mFile, "must have file");
-    NS_ASSERTION(aFileInfo, "must have file info");
-    // Lazily get the content type and size
-    mContentType.SetIsVoid(true);
-    mFile->GetLeafName(mName);
-
-    mFileInfos.AppendElement(aFileInfo);
-  }
-
   // Create as a file
   BlobImplFile(const nsAString& aName, const nsAString& aContentType,
                uint64_t aLength, nsIFile* aFile)
     : BlobImplBase(aName, aContentType, aLength, UINT64_MAX)
     , mFile(aFile)
     , mWholeFile(true)
-    , mStoredFile(false)
     , mIsTemporary(false)
   {
     NS_ASSERTION(mFile, "must have file");
   }
 
   BlobImplFile(const nsAString& aName, const nsAString& aContentType,
                uint64_t aLength, nsIFile* aFile,
                int64_t aLastModificationDate)
     : BlobImplBase(aName, aContentType, aLength, aLastModificationDate)
     , mFile(aFile)
     , mWholeFile(true)
-    , mStoredFile(false)
     , mIsTemporary(false)
   {
     NS_ASSERTION(mFile, "must have file");
   }
 
   // Create as a file with custom name
   BlobImplFile(nsIFile* aFile, const nsAString& aName,
                const nsAString& aContentType)
     : BlobImplBase(aName, aContentType, UINT64_MAX, INT64_MAX)
     , mFile(aFile)
     , mWholeFile(true)
-    , mStoredFile(false)
     , mIsTemporary(false)
   {
     NS_ASSERTION(mFile, "must have file");
     if (aContentType.IsEmpty()) {
       // Lazily get the content type and size
       mContentType.SetIsVoid(true);
     }
   }
 
-  // Create as a stored file
-  BlobImplFile(const nsAString& aName, const nsAString& aContentType,
-               uint64_t aLength, nsIFile* aFile,
-               indexedDB::FileInfo* aFileInfo)
-    : BlobImplBase(aName, aContentType, aLength, UINT64_MAX)
-    , mFile(aFile)
-    , mWholeFile(true)
-    , mStoredFile(true)
-    , mIsTemporary(false)
-  {
-    NS_ASSERTION(mFile, "must have file");
-    mFileInfos.AppendElement(aFileInfo);
-  }
-
-  // Create as a stored blob
-  BlobImplFile(const nsAString& aContentType, uint64_t aLength,
-               nsIFile* aFile, indexedDB::FileInfo* aFileInfo)
-    : BlobImplBase(aContentType, aLength)
-    , mFile(aFile)
-    , mWholeFile(true)
-    , mStoredFile(true)
-    , mIsTemporary(false)
-  {
-    NS_ASSERTION(mFile, "must have file");
-    mFileInfos.AppendElement(aFileInfo);
-  }
-
   // Create as a file to be later initialized
   BlobImplFile()
     : BlobImplBase(EmptyString(), EmptyString(), UINT64_MAX, INT64_MAX)
     , mWholeFile(true)
-    , mStoredFile(false)
     , mIsTemporary(false)
   {
     // Lazily get the content type and size
     mContentType.SetIsVoid(true);
     mName.SetIsVoid(true);
   }
 
   // Overrides
@@ -927,55 +814,27 @@ protected:
 
 private:
   // Create slice
   BlobImplFile(const BlobImplFile* aOther, uint64_t aStart,
                uint64_t aLength, const nsAString& aContentType)
     : BlobImplBase(aContentType, aOther->mStart + aStart, aLength)
     , mFile(aOther->mFile)
     , mWholeFile(false)
-    , mStoredFile(aOther->mStoredFile)
     , mIsTemporary(false)
   {
     NS_ASSERTION(mFile, "must have file");
     mImmutable = aOther->mImmutable;
-
-    if (mStoredFile) {
-      indexedDB::FileInfo* fileInfo;
-
-      using indexedDB::IndexedDatabaseManager;
-
-      if (IndexedDatabaseManager::IsClosed()) {
-        fileInfo = aOther->GetFileInfo();
-      }
-      else {
-        mozilla::MutexAutoLock lock(IndexedDatabaseManager::FileMutex());
-        fileInfo = aOther->GetFileInfo();
-      }
-
-      mFileInfos.AppendElement(fileInfo);
-    }
   }
 
   virtual already_AddRefed<BlobImpl>
   CreateSlice(uint64_t aStart, uint64_t aLength,
               const nsAString& aContentType, ErrorResult& aRv) override;
 
-  virtual bool IsStoredFile() const override
-  {
-    return mStoredFile;
-  }
-
-  virtual bool IsWholeFile() const override
-  {
-    return mWholeFile;
-  }
-
   nsCOMPtr<nsIFile> mFile;
   bool mWholeFile;
-  bool mStoredFile;
   bool mIsTemporary;
 };
 
 } // namespace dom
 } // namespace mozilla
 
 #endif // mozilla_dom_File_h

--- a/dom/base/StructuredCloneHelper.h
+++ b/dom/base/StructuredCloneHelper.h
@@ -6,16 +6,20 @@
 #ifndef mozilla_dom_StructuredCloneHelper_h
 #define mozilla_dom_StructuredCloneHelper_h
 
 #include "js/StructuredClone.h"
 #include "nsAutoPtr.h"
 #include "nsISupports.h"
 #include "nsTArray.h"
 
+#ifdef DEBUG
+#include "nsIThread.h"
+#endif
+
 namespace mozilla {
 class ErrorResult;
 namespace layers {
 class Image;
 }
 
 namespace dom {
 
@@ -162,38 +166,16 @@ public:
             ErrorResult &aRv);
 
   // Sometimes, when IPC is involved, you must send a buffer after a Write().
   // This method 'steals' the internal data from this helper class.
   // You should free this buffer with FreeBuffer().
   void MoveBufferDataToArray(FallibleTArray<uint8_t>& aArray,
                              ErrorResult& aRv);
 
-  // If you receive a buffer from IPC, you can use this method to retrieve a
-  // JS::Value. It can happen that you want to pre-populate the array of Blobs
-  // and/or the PortIdentifiers.
-  void ReadFromBuffer(nsISupports* aParent,
-                      JSContext* aCx,
-                      uint64_t* aBuffer,
-                      size_t aBufferLength,
-                      JS::MutableHandle<JS::Value> aValue,
-                      ErrorResult &aRv);
-
-  void ReadFromBuffer(nsISupports* aParent,
-                      JSContext* aCx,
-                      uint64_t* aBuffer,
-                      size_t aBufferLength,
-                      uint32_t aAlgorithmVersion,
-                      JS::MutableHandle<JS::Value> aValue,
-                      ErrorResult &aRv);
-
-  // Use this method to free a buffer generated by MoveToBuffer().
-  void FreeBuffer(uint64_t* aBuffer,
-                  size_t aBufferLength);
-
   bool HasClonedDOMObjects() const
   {
     return !mBlobImplArray.IsEmpty() ||
            !mClonedImages.IsEmpty();
   }
 
   nsTArray<nsRefPtr<BlobImpl>>& BlobImpls()
   {
@@ -252,16 +234,38 @@ public:
                                      void** aContent,
                                      uint64_t* aExtraData) override;
 
   virtual void FreeTransferCallback(uint32_t aTag,
                                     JS::TransferableOwnership aOwnership,
                                     void* aContent,
                                     uint64_t aExtraData) override;
 protected:
+  // If you receive a buffer from IPC, you can use this method to retrieve a
+  // JS::Value. It can happen that you want to pre-populate the array of Blobs
+  // and/or the PortIdentifiers.
+  void ReadFromBuffer(nsISupports* aParent,
+                      JSContext* aCx,
+                      uint64_t* aBuffer,
+                      size_t aBufferLength,
+                      JS::MutableHandle<JS::Value> aValue,
+                      ErrorResult &aRv);
+
+  void ReadFromBuffer(nsISupports* aParent,
+                      JSContext* aCx,
+                      uint64_t* aBuffer,
+                      size_t aBufferLength,
+                      uint32_t aAlgorithmVersion,
+                      JS::MutableHandle<JS::Value> aValue,
+                      ErrorResult &aRv);
+
+  // Use this method to free a buffer generated by MoveToBuffer().
+  void FreeBuffer(uint64_t* aBuffer,
+                  size_t aBufferLength);
+
   bool mSupportsCloning;
   bool mSupportsTransferring;
   ContextSupport mContext;
 
   // Useful for the structured clone algorithm:
 
   nsTArray<nsRefPtr<BlobImpl>> mBlobImplArray;
 

--- a/dom/base/nsFrameMessageManager.cpp
+++ b/dom/base/nsFrameMessageManager.cpp
@@ -758,17 +758,17 @@ nsFrameMessageManager::SendMessage(const
     return NS_ERROR_DOM_DATA_CLONE_ERR;
   }
 
   JS::Rooted<JSObject*> objects(aCx);
   if (aArgc >= 3 && aObjects.isObject()) {
     objects = &aObjects.toObject();
   }
 
-  nsTArray<OwningSerializedStructuredCloneBuffer> retval;
+  nsTArray<StructuredCloneIPCHelper> retval;
 
   sSendingSyncMessage |= aIsSync;
   bool ok = mCallback->DoSendBlockingMessage(aCx, aMessageName, helper, objects,
                                              aPrincipal, &retval, aIsSync);
   if (aIsSync) {
     sSendingSyncMessage = false;
   }
 
@@ -777,18 +777,19 @@ nsFrameMessageManager::SendMessage(const
   }
 
   uint32_t len = retval.Length();
   JS::Rooted<JSObject*> dataArray(aCx, JS_NewArrayObject(aCx, len));
   NS_ENSURE_TRUE(dataArray, NS_ERROR_OUT_OF_MEMORY);
 
   for (uint32_t i = 0; i < len; ++i) {
     JS::Rooted<JS::Value> ret(aCx);
-    if (!JS_ReadStructuredClone(aCx, retval[i].data, retval[i].dataLength,
-                                JS_STRUCTURED_CLONE_VERSION, &ret, nullptr, nullptr)) {
+    ErrorResult rv;
+    retval[i].Read(aCx, &ret, rv);
+    if (rv.Failed()) {
       MOZ_ASSERT(false, "Unable to read structured clone in SendMessage");
       return NS_ERROR_UNEXPECTED;
     }
 
     NS_ENSURE_TRUE(JS_DefineElement(aCx, dataArray, i, ret, JSPROP_ENUMERATE),
                    NS_ERROR_OUT_OF_MEMORY);
   }
 
@@ -1067,32 +1068,32 @@ public:
 nsresult
 nsFrameMessageManager::ReceiveMessage(nsISupports* aTarget,
                                       nsIFrameLoader* aTargetFrameLoader,
                                       const nsAString& aMessage,
                                       bool aIsSync,
                                       StructuredCloneIPCHelper* aCloneHelper,
                                       mozilla::jsipc::CpowHolder* aCpows,
                                       nsIPrincipal* aPrincipal,
-                                      nsTArray<OwningSerializedStructuredCloneBuffer>* aRetVal)
+                                      nsTArray<StructuredCloneIPCHelper>* aRetVal)
 {
   return ReceiveMessage(aTarget, aTargetFrameLoader, mClosed, aMessage, aIsSync,
                         aCloneHelper, aCpows, aPrincipal, aRetVal);
 }
 
 nsresult
 nsFrameMessageManager::ReceiveMessage(nsISupports* aTarget,
                                       nsIFrameLoader* aTargetFrameLoader,
                                       bool aTargetClosed,
                                       const nsAString& aMessage,
                                       bool aIsSync,
                                       StructuredCloneIPCHelper* aCloneHelper,
                                       mozilla::jsipc::CpowHolder* aCpows,
                                       nsIPrincipal* aPrincipal,
-                                      nsTArray<OwningSerializedStructuredCloneBuffer>* aRetVal)
+                                      nsTArray<StructuredCloneIPCHelper>* aRetVal)
 {
   nsAutoTObserverArray<nsMessageListenerInfo, 1>* listeners =
     mListeners.Get(aMessage);
   if (listeners) {
 
     MMListenerRemover lr(this);
 
     nsAutoTObserverArray<nsMessageListenerInfo, 1>::EndLimitedIterator
@@ -1261,34 +1262,34 @@ nsFrameMessageManager::ReceiveMessage(ns
           return NS_ERROR_UNEXPECTED;
         }
 
         if (!JS_CallFunctionValue(cx, thisObject, funval,
                                   JS::HandleValueArray(argv), &rval)) {
           continue;
         }
         if (aRetVal) {
-          JSAutoStructuredCloneBuffer buffer;
-          if (!buffer.write(cx, rval)) {
+          ErrorResult rv;
+          StructuredCloneIPCHelper* helper = aRetVal->AppendElement();
+          helper->Write(cx, rval, rv);
+          if (NS_WARN_IF(rv.Failed())) {
+            aRetVal->RemoveElementAt(aRetVal->Length() - 1);
             nsString msg = aMessage + NS_LITERAL_STRING(": message reply cannot be cloned. Are you trying to send an XPCOM object?");
 
             nsCOMPtr<nsIConsoleService> console(do_GetService(NS_CONSOLESERVICE_CONTRACTID));
             if (console) {
               nsCOMPtr<nsIScriptError> error(do_CreateInstance(NS_SCRIPTERROR_CONTRACTID));
               error->Init(msg, EmptyString(), EmptyString(),
                           0, 0, nsIScriptError::warningFlag, "chrome javascript");
               console->LogMessage(error);
             }
 
             JS_ClearPendingException(cx);
             continue;
           }
-
-          OwningSerializedStructuredCloneBuffer* data = aRetVal->AppendElement();
-          buffer.steal(&data->data, &data->dataLength);
         }
       }
     }
   }
   nsRefPtr<nsFrameMessageManager> kungfuDeathGrip = mParentManager;
   return mParentManager ? mParentManager->ReceiveMessage(aTarget, aTargetFrameLoader,
                                                          aTargetClosed, aMessage,
                                                          aIsSync, aCloneHelper,
@@ -1989,17 +1990,17 @@ public:
     MOZ_COUNT_DTOR(ChildProcessMessageManagerCallback);
   }
 
   virtual bool DoSendBlockingMessage(JSContext* aCx,
                                      const nsAString& aMessage,
                                      StructuredCloneIPCHelper& aHelper,
                                      JS::Handle<JSObject *> aCpows,
                                      nsIPrincipal* aPrincipal,
-                                     nsTArray<OwningSerializedStructuredCloneBuffer>* aRetVal,
+                                     nsTArray<StructuredCloneIPCHelper>* aRetVal,
                                      bool aIsSync) override
   {
     mozilla::dom::ContentChild* cc =
       mozilla::dom::ContentChild::GetSingleton();
     if (!cc) {
       return true;
     }
     ClonedMessageData data;
@@ -2080,17 +2081,17 @@ public:
     MOZ_COUNT_DTOR(SameChildProcessMessageManagerCallback);
   }
 
   virtual bool DoSendBlockingMessage(JSContext* aCx,
                                      const nsAString& aMessage,
                                      StructuredCloneIPCHelper& aHelper,
                                      JS::Handle<JSObject *> aCpows,
                                      nsIPrincipal* aPrincipal,
-                                     nsTArray<OwningSerializedStructuredCloneBuffer>* aRetVal,
+                                     nsTArray<StructuredCloneIPCHelper>* aRetVal,
                                      bool aIsSync) override
   {
     SameProcessMessageQueue* queue = SameProcessMessageQueue::Get();
     queue->Flush();
 
     if (nsFrameMessageManager::sSameProcessParentManager) {
       SameProcessCpowHolder cpows(js::GetRuntime(aCx), aCpows);
       nsRefPtr<nsFrameMessageManager> ppm = nsFrameMessageManager::sSameProcessParentManager;

--- a/dom/base/nsFrameMessageManager.h
+++ b/dom/base/nsFrameMessageManager.h
@@ -29,19 +29,16 @@
 #include "nsTObserverArray.h"
 #include "mozilla/dom/SameProcessMessageQueue.h"
 #include "mozilla/dom/StructuredCloneIPCHelper.h"
 #include "mozilla/jsipc/CpowHolder.h"
 
 class nsIFrameLoader;
 
 namespace mozilla {
-
-struct OwningSerializedStructuredCloneBuffer;
-
 namespace dom {
 
 class nsIContentParent;
 class nsIContentChild;
 class ClonedMessageData;
 class MessageManagerReporter;
 
 namespace ipc {
@@ -52,33 +49,30 @@ enum MessageManagerFlags {
   MM_GLOBAL = 2,
   MM_PROCESSMANAGER = 4,
   MM_BROADCASTER = 8,
   MM_OWNSCALLBACK = 16
 };
 
 class MessageManagerCallback
 {
-protected:
-  typedef mozilla::OwningSerializedStructuredCloneBuffer OwningSerializedStructuredCloneBuffer;
-
 public:
   virtual ~MessageManagerCallback() {}
 
   virtual bool DoLoadMessageManagerScript(const nsAString& aURL, bool aRunInGlobalScope)
   {
     return true;
   }
 
   virtual bool DoSendBlockingMessage(JSContext* aCx,
                                      const nsAString& aMessage,
                                      StructuredCloneIPCHelper& aHelper,
                                      JS::Handle<JSObject*> aCpows,
                                      nsIPrincipal* aPrincipal,
-                                     nsTArray<OwningSerializedStructuredCloneBuffer>* aRetVal,
+                                     nsTArray<StructuredCloneIPCHelper>* aRetVal,
                                      bool aIsSync)
   {
     return true;
   }
 
   virtual bool DoSendAsyncMessage(JSContext* aCx,
                                   const nsAString& aMessage,
                                   StructuredCloneIPCHelper& aHelper,
@@ -165,17 +159,16 @@ private:
 class nsFrameMessageManager final : public nsIContentFrameMessageManager,
                                     public nsIMessageBroadcaster,
                                     public nsIFrameScriptLoader,
                                     public nsIGlobalProcessScriptLoader,
                                     public nsIProcessChecker
 {
   friend class mozilla::dom::MessageManagerReporter;
   typedef mozilla::dom::StructuredCloneIPCHelper StructuredCloneIPCHelper;
-  typedef mozilla::OwningSerializedStructuredCloneBuffer OwningSerializedStructuredCloneBuffer;
 public:
   nsFrameMessageManager(mozilla::dom::ipc::MessageManagerCallback* aCallback,
                         nsFrameMessageManager* aParentManager,
                         /* mozilla::dom::ipc::MessageManagerFlags */ uint32_t aFlags);
 
 private:
   ~nsFrameMessageManager();
 
@@ -196,17 +189,17 @@ public:
 
   static nsFrameMessageManager*
   NewProcessMessageManager(bool aIsRemote);
 
   nsresult ReceiveMessage(nsISupports* aTarget, nsIFrameLoader* aTargetFrameLoader,
                           const nsAString& aMessage,
                           bool aIsSync, StructuredCloneIPCHelper* aCloneHelper,
                           mozilla::jsipc::CpowHolder* aCpows, nsIPrincipal* aPrincipal,
-                          nsTArray<OwningSerializedStructuredCloneBuffer>* aRetVal);
+                          nsTArray<StructuredCloneIPCHelper>* aRetVal);
 
   void AddChildManager(nsFrameMessageManager* aManager);
   void RemoveChildManager(nsFrameMessageManager* aManager)
   {
     mChildManagers.RemoveObject(aManager);
   }
   void Disconnect(bool aRemoveFromParent = true);
   void Close();
@@ -264,17 +257,17 @@ private:
                        uint8_t aArgc,
                        JS::MutableHandle<JS::Value> aRetval,
                        bool aIsSync);
 
   nsresult ReceiveMessage(nsISupports* aTarget, nsIFrameLoader* aTargetFrameLoader,
                           bool aTargetClosed, const nsAString& aMessage,
                           bool aIsSync, StructuredCloneIPCHelper* aCloneHelper,
                           mozilla::jsipc::CpowHolder* aCpows, nsIPrincipal* aPrincipal,
-                          nsTArray<OwningSerializedStructuredCloneBuffer>* aRetVal);
+                          nsTArray<StructuredCloneIPCHelper>* aRetVal);
 
   NS_IMETHOD LoadScript(const nsAString& aURL,
                         bool aAllowDelayedLoad,
                         bool aRunInGlobalScope);
   NS_IMETHOD RemoveDelayedScript(const nsAString& aURL);
   NS_IMETHOD GetDelayedScripts(JSContext* aCx, JS::MutableHandle<JS::Value> aList);
 
 protected:

--- a/dom/base/nsInProcessTabChildGlobal.cpp
+++ b/dom/base/nsInProcessTabChildGlobal.cpp
@@ -23,17 +23,17 @@ using namespace mozilla;
 using namespace mozilla::dom;
 
 bool
 nsInProcessTabChildGlobal::DoSendBlockingMessage(JSContext* aCx,
                                                  const nsAString& aMessage,
                                                  StructuredCloneIPCHelper& aHelper,
                                                  JS::Handle<JSObject *> aCpows,
                                                  nsIPrincipal* aPrincipal,
-                                                 nsTArray<OwningSerializedStructuredCloneBuffer>* aRetVal,
+                                                 nsTArray<StructuredCloneIPCHelper>* aRetVal,
                                                  bool aIsSync)
 {
   SameProcessMessageQueue* queue = SameProcessMessageQueue::Get();
   queue->Flush();
 
   if (mChromeMessageManager) {
     SameProcessCpowHolder cpows(js::GetRuntime(aCx), aCpows);
     nsRefPtr<nsFrameMessageManager> mm = mChromeMessageManager;

--- a/dom/base/nsInProcessTabChildGlobal.h
+++ b/dom/base/nsInProcessTabChildGlobal.h
@@ -30,17 +30,17 @@ class EventChainPreVisitor;
 class nsInProcessTabChildGlobal : public mozilla::DOMEventTargetHelper,
                                   public nsMessageManagerScriptExecutor,
                                   public nsIInProcessContentFrameMessageManager,
                                   public nsIGlobalObject,
                                   public nsIScriptObjectPrincipal,
                                   public nsSupportsWeakReference,
                                   public mozilla::dom::ipc::MessageManagerCallback
 {
-  typedef mozilla::OwningSerializedStructuredCloneBuffer OwningSerializedStructuredCloneBuffer;
+  typedef mozilla::dom::StructuredCloneIPCHelper StructuredCloneIPCHelper;
 
 public:
   nsInProcessTabChildGlobal(nsIDocShell* aShell, nsIContent* aOwner,
                             nsFrameMessageManager* aChrome);
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(nsInProcessTabChildGlobal,
                                                          mozilla::DOMEventTargetHelper)
 
@@ -78,24 +78,24 @@ public:
 
   NS_DECL_NSIINPROCESSCONTENTFRAMEMESSAGEMANAGER
 
   /**
    * MessageManagerCallback methods that we override.
    */
   virtual bool DoSendBlockingMessage(JSContext* aCx,
                                       const nsAString& aMessage,
-                                      mozilla::dom::StructuredCloneIPCHelper& aHelper,
+                                      StructuredCloneIPCHelper& aHelper,
                                       JS::Handle<JSObject *> aCpows,
                                       nsIPrincipal* aPrincipal,
-                                      nsTArray<OwningSerializedStructuredCloneBuffer>* aRetVal,
+                                      nsTArray<StructuredCloneIPCHelper>* aRetVal,
                                       bool aIsSync) override;
   virtual bool DoSendAsyncMessage(JSContext* aCx,
                                   const nsAString& aMessage,
-                                  mozilla::dom::StructuredCloneIPCHelper& aHelper,
+                                  StructuredCloneIPCHelper& aHelper,
                                   JS::Handle<JSObject *> aCpows,
                                   nsIPrincipal* aPrincipal) override;
 
   virtual nsresult PreHandleEvent(
                      mozilla::EventChainPreVisitor& aVisitor) override;
   NS_IMETHOD AddEventListener(const nsAString& aType,
                               nsIDOMEventListener* aListener,
                               bool aUseCapture)

--- a/dom/base/nsStructuredCloneContainer.cpp
+++ b/dom/base/nsStructuredCloneContainer.cpp
@@ -11,125 +11,104 @@
 #include "nsIVariant.h"
 #include "nsIXPConnect.h"
 #include "nsServiceManagerUtils.h"
 #include "nsContentUtils.h"
 #include "jsapi.h"
 #include "xpcpublic.h"
 
 #include "mozilla/Base64.h"
-#include "mozilla/dom/StructuredCloneHelper.h"
 #include "mozilla/dom/ScriptSettings.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
 
 NS_IMPL_ADDREF(nsStructuredCloneContainer)
 NS_IMPL_RELEASE(nsStructuredCloneContainer)
 
 NS_INTERFACE_MAP_BEGIN(nsStructuredCloneContainer)
   NS_INTERFACE_MAP_ENTRY(nsIStructuredCloneContainer)
   NS_INTERFACE_MAP_ENTRY(nsISupports)
 NS_INTERFACE_MAP_END
 
 nsStructuredCloneContainer::nsStructuredCloneContainer()
-  : StructuredCloneHelper(CloningSupported, TransferringNotSupported,
-                          DifferentProcess)
-  , mState(eNotInitialized) , mData(nullptr), mSize(0), mVersion(0)
+  : mVersion(0)
 {
 }
 
 nsStructuredCloneContainer::~nsStructuredCloneContainer()
 {
-  if (mData) {
-    free(mData);
-  }
 }
 
 NS_IMETHODIMP
 nsStructuredCloneContainer::InitFromJSVal(JS::Handle<JS::Value> aData,
                                           JSContext* aCx)
 {
-  if (mState != eNotInitialized) {
+  if (DataLength()) {
     return NS_ERROR_FAILURE;
   }
 
   ErrorResult rv;
   Write(aCx, aData, rv);
   if (NS_WARN_IF(rv.Failed())) {
     return rv.StealNSResult();
   }
 
-  mState = eInitializedFromJSVal;
+  mVersion = JS_STRUCTURED_CLONE_VERSION;
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsStructuredCloneContainer::InitFromBase64(const nsAString &aData,
                                            uint32_t aFormatVersion,
                                            JSContext* aCx)
 {
-  if (mState != eNotInitialized) {
+  if (DataLength()) {
     return NS_ERROR_FAILURE;
   }
 
   NS_ConvertUTF16toUTF8 data(aData);
 
   nsAutoCString binaryData;
   nsresult rv = Base64Decode(data, binaryData);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  // Copy the string's data into our own buffer.
-  mData = (uint64_t*) malloc(binaryData.Length());
-  NS_ENSURE_STATE(mData);
-  memcpy(mData, binaryData.get(), binaryData.Length());
+  if (!CopyExternalData(binaryData.get(), binaryData.Length())) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
 
-  mSize = binaryData.Length();
   mVersion = aFormatVersion;
-
-  mState = eInitializedFromBase64;
   return NS_OK;
 }
 
 nsresult
 nsStructuredCloneContainer::DeserializeToJsval(JSContext* aCx,
                                                JS::MutableHandle<JS::Value> aValue)
 {
   aValue.setNull();
   JS::Rooted<JS::Value> jsStateObj(aCx);
 
-  if (mState == eInitializedFromJSVal) {
-    ErrorResult rv;
-    Read(nullptr, aCx, &jsStateObj, rv);
-    if (NS_WARN_IF(rv.Failed())) {
-      return rv.StealNSResult();
-    }
-  } else {
-    MOZ_ASSERT(mState == eInitializedFromBase64);
-    MOZ_ASSERT(mData);
-
-    ErrorResult rv;
-    ReadFromBuffer(nullptr, aCx, mData, mSize, mVersion, &jsStateObj, rv);
-    if (NS_WARN_IF(rv.Failed())) {
-      return rv.StealNSResult();
-    }
+  ErrorResult rv;
+  Read(aCx, &jsStateObj, rv);
+  if (NS_WARN_IF(rv.Failed())) {
+    return rv.StealNSResult();
   }
 
   aValue.set(jsStateObj);
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsStructuredCloneContainer::DeserializeToVariant(JSContext* aCx,
                                                  nsIVariant** aData)
 {
   NS_ENSURE_ARG_POINTER(aData);
   *aData = nullptr;
 
-  if (mState == eNotInitialized) {
+  if (!DataLength()) {
     return NS_ERROR_FAILURE;
   }
 
   // Deserialize to a JS::Value.
   JS::Rooted<JS::Value> jsStateObj(aCx);
   nsresult rv = DeserializeToJsval(aCx, &jsStateObj);
   if (NS_WARN_IF(NS_FAILED(rv))) {
     return rv;
@@ -146,83 +125,52 @@ nsStructuredCloneContainer::DeserializeT
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsStructuredCloneContainer::GetDataAsBase64(nsAString &aOut)
 {
   aOut.Truncate();
 
-  if (mState == eNotInitialized) {
+  if (!DataLength()) {
     return NS_ERROR_FAILURE;
   }
 
-  uint64_t* data;
-  size_t size;
-
-  if (mState == eInitializedFromJSVal) {
-    if (HasClonedDOMObjects()) {
-      return NS_ERROR_FAILURE;
-    }
-
-    data = BufferData();
-    size = BufferSize();
-  } else {
-    MOZ_ASSERT(mState == eInitializedFromBase64);
-    MOZ_ASSERT(mData);
-
-    data = mData;
-    size = mSize;
+  if (HasClonedDOMObjects()) {
+    return NS_ERROR_FAILURE;
   }
 
-  nsAutoCString binaryData(reinterpret_cast<char*>(data), size);
+  nsAutoCString binaryData(reinterpret_cast<char*>(Data()), DataLength());
   nsAutoCString base64Data;
   nsresult rv = Base64Encode(binaryData, base64Data);
   if (NS_WARN_IF(NS_FAILED(rv))) {
     return rv;
   }
 
   CopyASCIItoUTF16(base64Data, aOut);
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsStructuredCloneContainer::GetSerializedNBytes(uint64_t* aSize)
 {
   NS_ENSURE_ARG_POINTER(aSize);
 
-  if (mState == eNotInitialized) {
+  if (!DataLength()) {
     return NS_ERROR_FAILURE;
   }
 
-  if (mState == eInitializedFromJSVal) {
-    *aSize = BufferSize();
-    return NS_OK;
-  }
-
-  MOZ_ASSERT(mState == eInitializedFromBase64);
-
-  // mSize is a size_t, while aSize is a uint64_t.  We rely on an implicit cast
-  // here so that we'll get a compile error if a size_t-to-uint64_t cast is
-  // narrowing.
-  *aSize = mSize;
-
+  *aSize = DataLength();
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsStructuredCloneContainer::GetFormatVersion(uint32_t* aFormatVersion)
 {
   NS_ENSURE_ARG_POINTER(aFormatVersion);
 
-  if (mState == eNotInitialized) {
+  if (!DataLength()) {
     return NS_ERROR_FAILURE;
   }
 
-  if (mState == eInitializedFromJSVal) {
-    *aFormatVersion = JS_STRUCTURED_CLONE_VERSION;
-    return NS_OK;
-  }
-
-  MOZ_ASSERT(mState == eInitializedFromBase64);
   *aFormatVersion = mVersion;
   return NS_OK;
 }

--- a/dom/base/nsStructuredCloneContainer.h
+++ b/dom/base/nsStructuredCloneContainer.h
@@ -4,47 +4,37 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef nsStructuredCloneContainer_h__
 #define nsStructuredCloneContainer_h__
 
 #include "nsIStructuredCloneContainer.h"
 #include "mozilla/Attributes.h"
-#include "mozilla/dom/StructuredCloneHelper.h"
+#include "mozilla/dom/StructuredCloneIPCHelper.h"
 
 #define NS_STRUCTUREDCLONECONTAINER_CONTRACTID \
   "@mozilla.org/docshell/structured-clone-container;1"
 #define NS_STRUCTUREDCLONECONTAINER_CID \
 { /* 38bd0634-0fd4-46f0-b85f-13ced889eeec */       \
   0x38bd0634,                                      \
   0x0fd4,                                          \
   0x46f0,                                          \
   {0xb8, 0x5f, 0x13, 0xce, 0xd8, 0x89, 0xee, 0xec} \
 }
 
 class nsStructuredCloneContainer final
   : public nsIStructuredCloneContainer
-  , public mozilla::dom::StructuredCloneHelper
+  , public mozilla::dom::StructuredCloneIPCHelper
 {
   public:
     nsStructuredCloneContainer();
 
     NS_DECL_ISUPPORTS
     NS_DECL_NSISTRUCTUREDCLONECONTAINER
 
   private:
     ~nsStructuredCloneContainer();
 
-    enum {
-      eNotInitialized = 0,
-      eInitializedFromJSVal,
-      eInitializedFromBase64,
-    } mState;
-
-    uint64_t* mData;
-
-    // This needs to be size_t rather than a PR-type so it matches the JS API.
-    size_t mSize;
     uint32_t mVersion;
 };
 
 #endif

--- a/dom/base/nsXMLHttpRequest.cpp
+++ b/dom/base/nsXMLHttpRequest.cpp
@@ -3099,18 +3099,23 @@ nsXMLHttpRequest::SetRequestHeader(const
     }
   }
 
   if (!mAlreadySetHeaders.Contains(header)) {
     // Case 2 above
     mergeHeaders = false;
   }
 
-  // Merge headers depending on what we decided above.
-  nsresult rv = httpChannel->SetRequestHeader(header, value, mergeHeaders);
+  nsresult rv;
+  if (value.IsEmpty()) {
+    rv = httpChannel->SetEmptyRequestHeader(header);
+  } else {
+    // Merge headers depending on what we decided above.
+    rv = httpChannel->SetRequestHeader(header, value, mergeHeaders);
+  }
   if (rv == NS_ERROR_INVALID_ARG) {
     return NS_ERROR_DOM_SYNTAX_ERR;
   }
   if (NS_SUCCEEDED(rv)) {
     // Remember that we've set this header, so subsequent set operations will merge values.
     mAlreadySetHeaders.PutEntry(nsCString(header));
 
     // We'll want to duplicate this header for any replacement channels (eg. on redirect)
@@ -3441,19 +3446,23 @@ nsXMLHttpRequest::OnRedirectVerifyCallba
   if (NS_SUCCEEDED(result)) {
     mChannel = mNewRedirectChannel;
 
     nsCOMPtr<nsIHttpChannel> httpChannel(do_QueryInterface(mChannel));
     if (httpChannel) {
       // Ensure all original headers are duplicated for the new channel (bug #553888)
       for (uint32_t i = mModifiedRequestHeaders.Length(); i > 0; ) {
         --i;
-        httpChannel->SetRequestHeader(mModifiedRequestHeaders[i].header,
-                                      mModifiedRequestHeaders[i].value,
-                                      false);
+        if (mModifiedRequestHeaders[i].value.IsEmpty()) {
+          httpChannel->SetEmptyRequestHeader(mModifiedRequestHeaders[i].header);
+        } else {
+          httpChannel->SetRequestHeader(mModifiedRequestHeaders[i].header,
+                                        mModifiedRequestHeaders[i].value,
+                                        false);
+        }
       }
     }
   } else {
     mErrorLoad = true;
   }
 
   mNewRedirectChannel = nullptr;
 

--- a/dom/broadcastchannel/BroadcastChannelChild.cpp
+++ b/dom/broadcastchannel/BroadcastChannelChild.cpp
@@ -6,17 +6,17 @@
 
 #include "BroadcastChannelChild.h"
 #include "BroadcastChannel.h"
 #include "jsapi.h"
 #include "mozilla/dom/ipc/BlobChild.h"
 #include "mozilla/dom/File.h"
 #include "mozilla/dom/MessageEvent.h"
 #include "mozilla/dom/MessageEventBinding.h"
-#include "mozilla/dom/StructuredCloneHelper.h"
+#include "mozilla/dom/StructuredCloneIPCHelper.h"
 #include "mozilla/dom/WorkerPrivate.h"
 #include "mozilla/dom/WorkerScope.h"
 #include "mozilla/dom/ScriptSettings.h"
 #include "mozilla/ipc/PBackgroundChild.h"
 #include "WorkerPrivate.h"
 
 namespace mozilla {
 
@@ -80,29 +80,27 @@ BroadcastChannelChild::RecvNotify(const 
     globalObject = workerPrivate->GlobalScope();
   }
 
   if (!globalObject || !jsapi.Init(globalObject)) {
     NS_WARNING("Failed to initialize AutoJSAPI object.");
     return true;
   }
 
-  JSContext* cx = jsapi.cx();
-  const SerializedStructuredCloneBuffer& buffer = aData.data();
-  StructuredCloneHelper cloneHelper(StructuredCloneHelper::CloningSupported,
-                                    StructuredCloneHelper::TransferringNotSupported,
-                                    StructuredCloneHelper::DifferentProcess);
-
+  StructuredCloneIPCHelper cloneHelper;
   cloneHelper.BlobImpls().AppendElements(blobs);
 
+  const SerializedStructuredCloneBuffer& buffer = aData.data();
+  cloneHelper.UseExternalData(buffer.data, buffer.dataLength);
+
+  JSContext* cx = jsapi.cx();
   JS::Rooted<JS::Value> value(cx, JS::NullValue());
   if (buffer.dataLength) {
     ErrorResult rv;
-    cloneHelper.ReadFromBuffer(mBC->GetParentObject(), cx,
-                               buffer.data, buffer.dataLength, &value, rv);
+    cloneHelper.Read(cx, &value, rv);
     if (NS_WARN_IF(rv.Failed())) {
       return true;
     }
   }
 
   RootedDictionary<MessageEventInit> init(cx);
   init.mBubbles = false;
   init.mCancelable = false;

--- a/dom/fetch/FetchDriver.cpp
+++ b/dom/fetch/FetchDriver.cpp
@@ -472,17 +472,21 @@ FetchDriver::HttpFetch(bool aCORSFlag, b
       FailWithNetworkError();
       return rv;
     }
 
     // Set the same headers.
     nsAutoTArray<InternalHeaders::Entry, 5> headers;
     mRequest->Headers()->GetEntries(headers);
     for (uint32_t i = 0; i < headers.Length(); ++i) {
-      httpChan->SetRequestHeader(headers[i].mName, headers[i].mValue, false /* merge */);
+      if (headers[i].mValue.IsEmpty()) {
+        httpChan->SetEmptyRequestHeader(headers[i].mName);
+      } else {
+        httpChan->SetRequestHeader(headers[i].mName, headers[i].mValue, false /* merge */);
+      }
     }
 
     // Step 2. Set the referrer.
     nsAutoString referrer;
     mRequest->GetReferrer(referrer);
     if (referrer.EqualsLiteral(kFETCH_CLIENT_REFERRER_STR)) {
       rv = nsContentUtils::SetFetchReferrerURIWithPolicy(mPrincipal,
                                                          mDocument,

new file mode 100644
--- /dev/null
+++ b/dom/filehandle/ActorsChild.cpp
@@ -0,0 +1,743 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ActorsChild.h"
+
+#include "BackgroundChildImpl.h"
+#include "FileHandleBase.h"
+#include "FileRequestBase.h"
+#include "js/Date.h"
+#include "mozilla/dom/EncodingUtils.h"
+#include "mozilla/dom/File.h"
+#include "mozilla/dom/ipc/BlobChild.h"
+#include "MutableFileBase.h"
+#include "nsCOMPtr.h"
+#include "nsContentUtils.h"
+#include "nsString.h"
+#include "xpcpublic.h"
+
+namespace mozilla {
+namespace dom {
+
+/*******************************************************************************
+ * Helpers
+ ******************************************************************************/
+
+namespace {
+
+class MOZ_STACK_CLASS AutoSetCurrentFileHandle final
+{
+  typedef mozilla::ipc::BackgroundChildImpl BackgroundChildImpl;
+
+  FileHandleBase* const mFileHandle;
+  FileHandleBase* mPreviousFileHandle;
+  FileHandleBase** mThreadLocalSlot;
+
+public:
+  explicit AutoSetCurrentFileHandle(FileHandleBase* aFileHandle)
+    : mFileHandle(aFileHandle)
+    , mPreviousFileHandle(nullptr)
+    , mThreadLocalSlot(nullptr)
+  {
+    if (aFileHandle) {
+      BackgroundChildImpl::ThreadLocal* threadLocal =
+        BackgroundChildImpl::GetThreadLocalForCurrentThread();
+      MOZ_ASSERT(threadLocal);
+
+      // Hang onto this location for resetting later.
+      mThreadLocalSlot = &threadLocal->mCurrentFileHandle;
+
+      // Save the current value.
+      mPreviousFileHandle = *mThreadLocalSlot;
+
+      // Set the new value.
+      *mThreadLocalSlot = aFileHandle;
+    }
+  }
+
+  ~AutoSetCurrentFileHandle()
+  {
+    MOZ_ASSERT_IF(mThreadLocalSlot, mFileHandle);
+    MOZ_ASSERT_IF(mThreadLocalSlot, *mThreadLocalSlot == mFileHandle);
+
+    if (mThreadLocalSlot) {
+      // Reset old value.
+      *mThreadLocalSlot = mPreviousFileHandle;
+    }
+  }
+
+  FileHandleBase*
+  FileHandle() const
+  {
+    return mFileHandle;
+  }
+};
+
+class MOZ_STACK_CLASS ResultHelper final
+  : public FileRequestBase::ResultCallback
+{
+  FileRequestBase* mFileRequest;
+  AutoSetCurrentFileHandle mAutoFileHandle;
+
+  union
+  {
+    File* mFile;
+    const nsCString* mString;
+    const FileRequestMetadata* mMetadata;
+    const JS::Handle<JS::Value>* mJSValHandle;
+  } mResult;
+
+  enum
+  {
+    ResultTypeFile,
+    ResultTypeString,
+    ResultTypeMetadata,
+    ResultTypeJSValHandle,
+  } mResultType;
+
+public:
+  ResultHelper(FileRequestBase* aFileRequest,
+               FileHandleBase* aFileHandle,
+               File* aResult)
+    : mFileRequest(aFileRequest)
+    , mAutoFileHandle(aFileHandle)
+    , mResultType(ResultTypeFile)
+  {
+    MOZ_ASSERT(aFileRequest);
+    MOZ_ASSERT(aFileHandle);
+    MOZ_ASSERT(aResult);
+
+    mResult.mFile = aResult;
+  }
+
+  ResultHelper(FileRequestBase* aFileRequest,
+               FileHandleBase* aFileHandle,
+               const nsCString* aResult)
+    : mFileRequest(aFileRequest)
+    , mAutoFileHandle(aFileHandle)
+    , mResultType(ResultTypeString)
+  {
+    MOZ_ASSERT(aFileRequest);
+    MOZ_ASSERT(aFileHandle);
+    MOZ_ASSERT(aResult);
+
+    mResult.mString = aResult;
+  }
+
+  ResultHelper(FileRequestBase* aFileRequest,
+               FileHandleBase* aFileHandle,
+               const FileRequestMetadata* aResult)
+    : mFileRequest(aFileRequest)
+    , mAutoFileHandle(aFileHandle)
+    , mResultType(ResultTypeMetadata)
+  {
+    MOZ_ASSERT(aFileRequest);
+    MOZ_ASSERT(aFileHandle);
+    MOZ_ASSERT(aResult);
+
+    mResult.mMetadata = aResult;
+  }
+
+
+  ResultHelper(FileRequestBase* aFileRequest,
+               FileHandleBase* aFileHandle,
+               const JS::Handle<JS::Value>* aResult)
+    : mFileRequest(aFileRequest)
+    , mAutoFileHandle(aFileHandle)
+    , mResultType(ResultTypeJSValHandle)
+  {
+    MOZ_ASSERT(aFileRequest);
+    MOZ_ASSERT(aFileHandle);
+    MOZ_ASSERT(aResult);
+
+    mResult.mJSValHandle = aResult;
+  }
+
+  FileRequestBase*
+  FileRequest() const
+  {
+    return mFileRequest;
+  }
+
+  FileHandleBase*
+  FileHandle() const
+  {
+    return mAutoFileHandle.FileHandle();
+  }
+
+  virtual nsresult
+  GetResult(JSContext* aCx, JS::MutableHandle<JS::Value> aResult) override
+  {
+    MOZ_ASSERT(aCx);
+    MOZ_ASSERT(mFileRequest);
+
+    switch (mResultType) {
+      case ResultTypeFile:
+        return GetResult(aCx, mResult.mFile, aResult);
+
+      case ResultTypeString:
+        return GetResult(aCx, mResult.mString, aResult);
+
+      case ResultTypeMetadata:
+        return GetResult(aCx, mResult.mMetadata, aResult);
+
+      case ResultTypeJSValHandle:
+        aResult.set(*mResult.mJSValHandle);
+        return NS_OK;
+
+      default:
+        MOZ_CRASH("Unknown result type!");
+    }
+
+    MOZ_CRASH("Should never get here!");
+  }
+
+private:
+  nsresult
+  GetResult(JSContext* aCx,
+            File* aFile,
+            JS::MutableHandle<JS::Value> aResult)
+  {
+    bool ok = GetOrCreateDOMReflector(aCx, aFile, aResult);
+    if (NS_WARN_IF(!ok)) {
+      return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+
+    return NS_OK;
+  }
+
+  nsresult
+  GetResult(JSContext* aCx,
+            const nsCString* aString,
+            JS::MutableHandle<JS::Value> aResult)
+  {
+    const nsCString& data = *aString;
+
+    nsresult rv;
+
+    if (!mFileRequest->HasEncoding()) {
+      JS::Rooted<JSObject*> arrayBuffer(aCx);
+      rv = nsContentUtils::CreateArrayBuffer(aCx, data, arrayBuffer.address());
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+      }
+
+      aResult.setObject(*arrayBuffer);
+      return NS_OK;
+    }
+
+    nsAutoCString encoding;
+    // The BOM sniffing is baked into the "decode" part of the Encoding
+    // Standard, which the File API references.
+    if (!nsContentUtils::CheckForBOM(
+          reinterpret_cast<const unsigned char *>(data.get()),
+          data.Length(),
+          encoding)) {
+      // BOM sniffing failed. Try the API argument.
+      if (!EncodingUtils::FindEncodingForLabel(mFileRequest->GetEncoding(),
+                                               encoding)) {
+        // API argument failed. Since we are dealing with a file system file,
+        // we don't have a meaningful type attribute for the blob available,
+        // so proceeding to the next step, which is defaulting to UTF-8.
+        encoding.AssignLiteral("UTF-8");
+      }
+    }
+
+    nsString tmpString;
+    rv = nsContentUtils::ConvertStringFromEncoding(encoding, data, tmpString);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+
+    if (NS_WARN_IF(!xpc::StringToJsval(aCx, tmpString, aResult))) {
+      return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+
+    return NS_OK;
+  }
+
+  nsresult
+  GetResult(JSContext* aCx,
+            const FileRequestMetadata* aMetadata,
+            JS::MutableHandle<JS::Value> aResult)
+  {
+    JS::Rooted<JSObject*> obj(aCx, JS_NewPlainObject(aCx));
+    if (NS_WARN_IF(!obj)) {
+      return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+
+    const FileRequestSize& size = aMetadata->size();
+    if (size.type() != FileRequestSize::Tvoid_t) {
+      MOZ_ASSERT(size.type() == FileRequestSize::Tuint64_t);
+
+      JS::Rooted<JS::Value> number(aCx, JS_NumberValue(size.get_uint64_t()));
+
+      if (NS_WARN_IF(!JS_DefineProperty(aCx, obj, "size", number, 0))) {
+        return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+      }
+    }
+
+    const FileRequestLastModified& lastModified = aMetadata->lastModified();
+    if (lastModified.type() != FileRequestLastModified::Tvoid_t) {
+      MOZ_ASSERT(lastModified.type() == FileRequestLastModified::Tint64_t);
+
+      JS::Rooted<JSObject*> date(aCx,
+        JS::NewDateObject(aCx, JS::TimeClip(lastModified.get_int64_t())));
+      if (NS_WARN_IF(!date)) {
+        return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+      }
+
+      if (NS_WARN_IF(!JS_DefineProperty(aCx, obj, "lastModified", date, 0))) {
+        return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+      }
+    }
+
+    aResult.setObject(*obj);
+    return NS_OK;
+  }
+};
+
+already_AddRefed<File>
+ConvertActorToFile(FileHandleBase* aFileHandle,
+                   const FileRequestGetFileResponse& aResponse)
+{
+  auto* actor = static_cast<BlobChild*>(aResponse.fileChild());
+
+  MutableFileBase* mutableFile = aFileHandle->MutableFile();
+  MOZ_ASSERT(mutableFile);
+
+  const FileRequestMetadata& metadata = aResponse.metadata();
+
+  const FileRequestSize& size = metadata.size();
+  MOZ_ASSERT(size.type() == FileRequestSize::Tuint64_t);
+
+  const FileRequestLastModified& lastModified = metadata.lastModified();
+  MOZ_ASSERT(lastModified.type() == FileRequestLastModified::Tint64_t);
+
+  actor->SetMysteryBlobInfo(mutableFile->Name(),
+                            mutableFile->Type(),
+                            size.get_uint64_t(),
+                            lastModified.get_int64_t(),
+                            BlobDirState::eUnknownIfDir);
+
+  nsRefPtr<BlobImpl> blobImpl = actor->GetBlobImpl();
+  MOZ_ASSERT(blobImpl);
+
+  nsRefPtr<File> file = mutableFile->CreateFileFor(blobImpl, aFileHandle);
+  return file.forget();
+}
+
+void
+HandleSuccess(ResultHelper* aResultHelper)
+{
+  MOZ_ASSERT(aResultHelper);
+
+  nsRefPtr<FileRequestBase> fileRequest = aResultHelper->FileRequest();
+  MOZ_ASSERT(fileRequest);
+  fileRequest->AssertIsOnOwningThread();
+
+  nsRefPtr<FileHandleBase> fileHandle = aResultHelper->FileHandle();
+  MOZ_ASSERT(fileHandle);
+
+  if (fileHandle->IsAborted()) {
+    fileRequest->SetError(NS_ERROR_DOM_FILEHANDLE_ABORT_ERR);
+    return;
+  }
+
+  MOZ_ASSERT(fileHandle->IsOpen());
+
+  fileRequest->SetResultCallback(aResultHelper);
+
+  MOZ_ASSERT(fileHandle->IsOpen() || fileHandle->IsAborted());
+}
+
+void
+HandleError(FileRequestBase* aFileRequest,
+            nsresult aErrorCode,
+            FileHandleBase* aFileHandle)
+{
+  MOZ_ASSERT(aFileRequest);
+  aFileRequest->AssertIsOnOwningThread();
+  MOZ_ASSERT(NS_FAILED(aErrorCode));
+  MOZ_ASSERT(NS_ERROR_GET_MODULE(aErrorCode) == NS_ERROR_MODULE_DOM_FILEHANDLE);
+  MOZ_ASSERT(aFileHandle);
+
+  nsRefPtr<FileRequestBase> fileRequest = aFileRequest;
+  nsRefPtr<FileHandleBase> fileHandle = aFileHandle;
+
+  AutoSetCurrentFileHandle ascfh(aFileHandle);
+
+  fileRequest->SetError(aErrorCode);
+
+  MOZ_ASSERT(fileHandle->IsOpen() || fileHandle->IsAborted());
+}
+
+} // anonymous namespace
+
+/*******************************************************************************
+ * BackgroundMutableFileChildBase
+ ******************************************************************************/
+
+BackgroundMutableFileChildBase::BackgroundMutableFileChildBase(
+                                             DEBUGONLY(PRThread* aOwningThread))
+  : ThreadObject(DEBUGONLY(aOwningThread))
+  , mMutableFile(nullptr)
+{
+  AssertIsOnOwningThread();
+
+  MOZ_COUNT_CTOR(BackgroundMutableFileChildBase);
+}
+
+BackgroundMutableFileChildBase::~BackgroundMutableFileChildBase()
+{
+  AssertIsOnOwningThread();
+
+  MOZ_COUNT_DTOR(BackgroundMutableFileChildBase);
+}
+
+void
+BackgroundMutableFileChildBase::EnsureDOMObject()
+{
+  AssertIsOnOwningThread();
+
+  if (mTemporaryStrongMutableFile) {
+    return;
+  }
+
+  mTemporaryStrongMutableFile = CreateMutableFile();
+
+  MOZ_ASSERT(mTemporaryStrongMutableFile);
+  mTemporaryStrongMutableFile->AssertIsOnOwningThread();
+
+  mMutableFile = mTemporaryStrongMutableFile;
+}
+
+void
+BackgroundMutableFileChildBase::ReleaseDOMObject()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mTemporaryStrongMutableFile);
+  mTemporaryStrongMutableFile->AssertIsOnOwningThread();
+  MOZ_ASSERT(mMutableFile == mTemporaryStrongMutableFile);
+
+  mTemporaryStrongMutableFile = nullptr;
+}
+
+void
+BackgroundMutableFileChildBase::SendDeleteMeInternal()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mTemporaryStrongMutableFile);
+
+  if (mMutableFile) {
+    mMutableFile->ClearBackgroundActor();
+    mMutableFile = nullptr;
+
+    MOZ_ALWAYS_TRUE(PBackgroundMutableFileChild::SendDeleteMe());
+  }
+}
+
+void
+BackgroundMutableFileChildBase::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnOwningThread();
+
+  if (mMutableFile) {
+    mMutableFile->ClearBackgroundActor();
+    DEBUGONLY(mMutableFile = nullptr;)
+  }
+}
+
+PBackgroundFileHandleChild*
+BackgroundMutableFileChildBase::AllocPBackgroundFileHandleChild(
+                                                          const FileMode& aMode)
+{
+  MOZ_CRASH("PBackgroundFileHandleChild actors should be manually "
+            "constructed!");
+}
+
+bool
+BackgroundMutableFileChildBase::DeallocPBackgroundFileHandleChild(
+                                             PBackgroundFileHandleChild* aActor)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aActor);
+
+  delete static_cast<BackgroundFileHandleChild*>(aActor);
+  return true;
+}
+
+/*******************************************************************************
+ * BackgroundFileHandleChild
+ ******************************************************************************/
+
+BackgroundFileHandleChild::BackgroundFileHandleChild(
+                                             DEBUGONLY(PRThread* aOwningThread,)
+                                             FileHandleBase* aFileHandle)
+  : ThreadObject(DEBUGONLY(aOwningThread))
+  , mTemporaryStrongFileHandle(aFileHandle)
+  , mFileHandle(aFileHandle)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+  aFileHandle->AssertIsOnOwningThread();
+
+  MOZ_COUNT_CTOR(BackgroundFileHandleChild);
+}
+
+BackgroundFileHandleChild::~BackgroundFileHandleChild()
+{
+  AssertIsOnOwningThread();
+
+  MOZ_COUNT_DTOR(BackgroundFileHandleChild);
+}
+
+void
+BackgroundFileHandleChild::SendDeleteMeInternal()
+{
+  AssertIsOnOwningThread();
+
+  if (mFileHandle) {
+    NoteActorDestroyed();
+
+    MOZ_ALWAYS_TRUE(PBackgroundFileHandleChild::SendDeleteMe());
+  }
+}
+
+void
+BackgroundFileHandleChild::NoteActorDestroyed()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT_IF(mTemporaryStrongFileHandle, mFileHandle);
+
+  if (mFileHandle) {
+    mFileHandle->ClearBackgroundActor();
+
+    // Normally this would be DEBUG-only but NoteActorDestroyed is also called
+    // from SendDeleteMeInternal. In that case we're going to receive an actual
+    // ActorDestroy call later and we don't want to touch a dead object.
+    mTemporaryStrongFileHandle = nullptr;
+    mFileHandle = nullptr;
+  }
+}
+
+void
+BackgroundFileHandleChild::NoteComplete()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT_IF(mFileHandle, mTemporaryStrongFileHandle);
+
+  mTemporaryStrongFileHandle = nullptr;
+}
+
+void
+BackgroundFileHandleChild::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnOwningThread();
+
+  NoteActorDestroyed();
+}
+
+bool
+BackgroundFileHandleChild::RecvComplete(const bool& aAborted)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileHandle);
+
+  mFileHandle->HandleCompleteOrAbort(aAborted);
+
+  NoteComplete();
+  return true;
+}
+
+PBackgroundFileRequestChild*
+BackgroundFileHandleChild::AllocPBackgroundFileRequestChild(
+                                               const FileRequestParams& aParams)
+{
+  MOZ_CRASH("PBackgroundFileRequestChild actors should be manually "
+            "constructed!");
+}
+
+bool
+BackgroundFileHandleChild::DeallocPBackgroundFileRequestChild(
+                                            PBackgroundFileRequestChild* aActor)
+{
+  MOZ_ASSERT(aActor);
+
+  delete static_cast<BackgroundFileRequestChild*>(aActor);
+  return true;
+}
+
+/*******************************************************************************
+ * BackgroundFileRequestChild
+ ******************************************************************************/
+
+BackgroundFileRequestChild::BackgroundFileRequestChild(
+                                             DEBUGONLY(PRThread* aOwningThread,)
+                                             FileRequestBase* aFileRequest)
+  : ThreadObject(DEBUGONLY(aOwningThread))
+  , mFileRequest(aFileRequest)
+  , mFileHandle(aFileRequest->FileHandle())
+  , mActorDestroyed(false)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileRequest);
+  aFileRequest->AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileHandle);
+  mFileHandle->AssertIsOnOwningThread();
+
+  MOZ_COUNT_CTOR(BackgroundFileRequestChild);
+}
+
+BackgroundFileRequestChild::~BackgroundFileRequestChild()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mFileHandle);
+
+  MOZ_COUNT_DTOR(BackgroundFileRequestChild);
+}
+
+void
+BackgroundFileRequestChild::HandleResponse(nsresult aResponse)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(NS_FAILED(aResponse));
+  MOZ_ASSERT(NS_ERROR_GET_MODULE(aResponse) == NS_ERROR_MODULE_DOM_FILEHANDLE);
+  MOZ_ASSERT(mFileHandle);
+
+  HandleError(mFileRequest, aResponse, mFileHandle);
+}
+
+void
+BackgroundFileRequestChild::HandleResponse(
+                                    const FileRequestGetFileResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  nsRefPtr<File> file = ConvertActorToFile(mFileHandle, aResponse);
+
+  ResultHelper helper(mFileRequest, mFileHandle, file);
+
+  HandleSuccess(&helper);
+}
+
+void
+BackgroundFileRequestChild::HandleResponse(const nsCString& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  ResultHelper helper(mFileRequest, mFileHandle, &aResponse);
+
+  HandleSuccess(&helper);
+}
+
+void
+BackgroundFileRequestChild::HandleResponse(const FileRequestMetadata& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  ResultHelper helper(mFileRequest, mFileHandle, &aResponse);
+
+  HandleSuccess(&helper);
+}
+
+void
+BackgroundFileRequestChild::HandleResponse(JS::Handle<JS::Value> aResponse)
+{
+  AssertIsOnOwningThread();
+
+  ResultHelper helper(mFileRequest, mFileHandle, &aResponse);
+
+  HandleSuccess(&helper);
+}
+
+void
+BackgroundFileRequestChild::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnOwningThread();
+
+  MOZ_ASSERT(!mActorDestroyed);
+
+  mActorDestroyed = true;
+
+  if (mFileHandle) {
+    mFileHandle->AssertIsOnOwningThread();
+
+    mFileHandle->OnRequestFinished(/* aActorDestroyedNormally */
+                                   aWhy == Deletion);
+
+    DEBUGONLY(mFileHandle = nullptr;)
+  }
+}
+
+bool
+BackgroundFileRequestChild::Recv__delete__(const FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileRequest);
+  MOZ_ASSERT(mFileHandle);
+
+  if (mFileHandle->IsAborted()) {
+    // Always handle an "error" with ABORT_ERR if the file handle was aborted,
+    // even if the request succeeded or failed with another error.
+    HandleResponse(NS_ERROR_DOM_FILEHANDLE_ABORT_ERR);
+  } else {
+    switch (aResponse.type()) {
+      case FileRequestResponse::Tnsresult:
+        HandleResponse(aResponse.get_nsresult());
+        break;
+
+      case FileRequestResponse::TFileRequestGetFileResponse:
+        HandleResponse(aResponse.get_FileRequestGetFileResponse());
+        break;
+
+      case FileRequestResponse::TFileRequestReadResponse:
+        HandleResponse(aResponse.get_FileRequestReadResponse().data());
+        break;
+
+      case FileRequestResponse::TFileRequestWriteResponse:
+        HandleResponse(JS::UndefinedHandleValue);
+        break;
+
+      case FileRequestResponse::TFileRequestTruncateResponse:
+        HandleResponse(JS::UndefinedHandleValue);
+        break;
+
+      case FileRequestResponse::TFileRequestFlushResponse:
+        HandleResponse(JS::UndefinedHandleValue);
+        break;
+
+      case FileRequestResponse::TFileRequestGetMetadataResponse:
+        HandleResponse(aResponse.get_FileRequestGetMetadataResponse()
+                                .metadata());
+        break;
+
+      default:
+        MOZ_CRASH("Unknown response type!");
+    }
+  }
+
+  mFileHandle->OnRequestFinished(/* aActorDestroyedNormally */ true);
+
+  // Null this out so that we don't try to call OnRequestFinished() again in
+  // ActorDestroy.
+  mFileHandle = nullptr;
+
+  return true;
+}
+
+bool
+BackgroundFileRequestChild::RecvProgress(const uint64_t& aProgress,
+                                         const uint64_t& aProgressMax)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileRequest);
+
+  mFileRequest->OnProgress(aProgress, aProgressMax);
+
+  return true;
+}
+
+} // namespace dom
+} // namespace mozilla

new file mode 100644
--- /dev/null
+++ b/dom/filehandle/ActorsChild.h
@@ -0,0 +1,175 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_filehandle_ActorsChild_h
+#define mozilla_dom_filehandle_ActorsChild_h
+
+#include "js/RootingAPI.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/FileHandleCommon.h"
+#include "mozilla/dom/PBackgroundFileHandleChild.h"
+#include "mozilla/dom/PBackgroundFileRequestChild.h"
+#include "mozilla/dom/PBackgroundMutableFileChild.h"
+#include "nsAutoPtr.h"
+
+class nsCString;
+
+namespace mozilla {
+namespace dom {
+
+class FileHandleBase;
+class FileRequestBase;
+class MutableFileBase;
+
+class BackgroundMutableFileChildBase
+  : public ThreadObject
+  , public PBackgroundMutableFileChild
+{
+protected:
+  friend class MutableFileBase;
+
+  nsRefPtr<MutableFileBase> mTemporaryStrongMutableFile;
+  MutableFileBase* mMutableFile;
+
+public:
+  void
+  EnsureDOMObject();
+
+  MutableFileBase*
+  GetDOMObject() const
+  {
+    AssertIsOnOwningThread();
+    return mMutableFile;
+  }
+
+  void
+  ReleaseDOMObject();
+
+protected:
+  BackgroundMutableFileChildBase(DEBUGONLY(PRThread* aOwningThread));
+
+  ~BackgroundMutableFileChildBase();
+
+  void
+  SendDeleteMeInternal();
+
+  virtual already_AddRefed<MutableFileBase>
+  CreateMutableFile() = 0;
+
+  // IPDL methods are only called by IPDL.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+
+  virtual PBackgroundFileHandleChild*
+  AllocPBackgroundFileHandleChild(const FileMode& aMode) override;
+
+  virtual bool
+  DeallocPBackgroundFileHandleChild(PBackgroundFileHandleChild* aActor)
+                                    override;
+
+  bool
+  SendDeleteMe() = delete;
+};
+
+class BackgroundFileHandleChild
+  : public ThreadObject
+  , public PBackgroundFileHandleChild
+{
+  friend class BackgroundMutableFileChildBase;
+  friend class MutableFileBase;
+
+  // mTemporaryStrongFileHandle is strong and is only valid until the end of
+  // NoteComplete() member function or until the NoteActorDestroyed() member
+  // function is called.
+  nsRefPtr<FileHandleBase> mTemporaryStrongFileHandle;
+
+  // mFileHandle is weak and is valid until the NoteActorDestroyed() member
+  // function is called.
+  FileHandleBase* mFileHandle;
+
+public:
+  BackgroundFileHandleChild(DEBUGONLY(PRThread* aOwningThread,)
+                            FileHandleBase* aFileHandle);
+
+  void
+  SendDeleteMeInternal();
+
+private:
+  ~BackgroundFileHandleChild();
+
+  void
+  NoteActorDestroyed();
+
+  void
+  NoteComplete();
+
+  // IPDL methods are only called by IPDL.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+
+  bool
+  RecvComplete(const bool& aAborted) override;
+
+  virtual PBackgroundFileRequestChild*
+  AllocPBackgroundFileRequestChild(const FileRequestParams& aParams)
+                                   override;
+
+  virtual bool
+  DeallocPBackgroundFileRequestChild(PBackgroundFileRequestChild* aActor)
+                                     override;
+
+  bool
+  SendDeleteMe() = delete;
+};
+
+class BackgroundFileRequestChild final
+  : public ThreadObject
+  , public PBackgroundFileRequestChild
+{
+  friend class BackgroundFileHandleChild;
+  friend class FileHandleBase;
+
+  nsRefPtr<FileRequestBase> mFileRequest;
+  nsRefPtr<FileHandleBase> mFileHandle;
+  bool mActorDestroyed;
+
+private:
+  // Only created by FileHandleBase.
+  BackgroundFileRequestChild(DEBUGONLY(PRThread* aOwningThread,)
+                             FileRequestBase* aFileRequest);
+
+  // Only destroyed by BackgroundFileHandleChild.
+  ~BackgroundFileRequestChild();
+
+  void
+  HandleResponse(nsresult aResponse);
+
+  void
+  HandleResponse(const FileRequestGetFileResponse& aResponse);
+
+  void
+  HandleResponse(const nsCString& aResponse);
+
+  void
+  HandleResponse(const FileRequestMetadata& aResponse);
+
+  void
+  HandleResponse(JS::Handle<JS::Value> aResponse);
+
+  // IPDL methods are only called by IPDL.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+
+  virtual bool
+  Recv__delete__(const FileRequestResponse& aResponse) override;
+
+  virtual bool
+  RecvProgress(const uint64_t& aProgress,
+               const uint64_t& aProgressMax) override;
+};
+
+} // namespace dom
+} // namespace mozilla
+
+#endif // mozilla_dom_filehandle_ActorsChild_h

new file mode 100644
--- /dev/null
+++ b/dom/filehandle/ActorsParent.cpp
@@ -0,0 +1,2664 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ActorsParent.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/unused.h"
+#include "mozilla/dom/File.h"
+#include "mozilla/dom/FileHandleCommon.h"
+#include "mozilla/dom/PBackgroundFileHandleParent.h"
+#include "mozilla/dom/PBackgroundFileRequestParent.h"
+#include "mozilla/dom/indexedDB/ActorsParent.h"
+#include "mozilla/dom/ipc/BlobParent.h"
+#include "nsComponentManagerUtils.h"
+#include "nsDebug.h"
+#include "nsError.h"
+#include "nsIEventTarget.h"
+#include "nsIFileStreams.h"
+#include "nsIInputStream.h"
+#include "nsIOutputStream.h"
+#include "nsIRunnable.h"
+#include "nsISeekableStream.h"
+#include "nsIThread.h"
+#include "nsIThreadPool.h"
+#include "nsNetUtil.h"
+#include "nsStreamUtils.h"
+#include "nsStringStream.h"
+#include "nsTArray.h"
+#include "nsThreadPool.h"
+#include "nsThreadUtils.h"
+#include "nsXPCOMCIDInternal.h"
+
+#define DISABLE_ASSERTS_FOR_FUZZING 0
+
+#if DISABLE_ASSERTS_FOR_FUZZING
+#define ASSERT_UNLESS_FUZZING(...) do { } while (0)
+#else
+#define ASSERT_UNLESS_FUZZING(...) MOZ_ASSERT(false, __VA_ARGS__)
+#endif
+
+namespace mozilla {
+namespace dom {
+
+using namespace mozilla::ipc;
+
+namespace {
+
+/******************************************************************************
+ * Constants
+ ******************************************************************************/
+
+const uint32_t kThreadLimit = 5;
+const uint32_t kIdleThreadLimit = 1;
+const uint32_t kIdleThreadTimeoutMs = 30000;
+
+const uint32_t kStreamCopyBlockSize = 32768;
+
+} // namespace
+
+class FileHandleThreadPool::FileHandleQueue final
+  : public nsRunnable
+{
+  friend class FileHandleThreadPool;
+
+  nsRefPtr<FileHandleThreadPool> mOwningFileHandleThreadPool;
+  nsRefPtr<FileHandle> mFileHandle;
+  nsTArray<nsRefPtr<FileHandleOp>> mQueue;
+  nsRefPtr<FileHandleOp> mCurrentOp;
+  bool mShouldFinish;
+
+public:
+  explicit
+  FileHandleQueue(FileHandleThreadPool* aFileHandleThreadPool,
+                  FileHandle* aFileHandle);
+
+  void
+  Enqueue(FileHandleOp* aFileHandleOp);
+
+  void
+  Finish();
+
+  void
+  ProcessQueue();
+
+private:
+  ~FileHandleQueue() {}
+
+  NS_DECL_NSIRUNNABLE
+};
+
+struct FileHandleThreadPool::DelayedEnqueueInfo
+{
+  nsRefPtr<FileHandle> mFileHandle;
+  nsRefPtr<FileHandleOp> mFileHandleOp;
+  bool mFinish;
+};
+
+class FileHandleThreadPool::DirectoryInfo
+{
+  friend class FileHandleThreadPool;
+
+  nsRefPtr<FileHandleThreadPool> mOwningFileHandleThreadPool;
+  nsTArray<nsRefPtr<FileHandleQueue>> mFileHandleQueues;
+  nsTArray<DelayedEnqueueInfo> mDelayedEnqueueInfos;
+  nsTHashtable<nsStringHashKey> mFilesReading;
+  nsTHashtable<nsStringHashKey> mFilesWriting;
+
+public:
+  FileHandleQueue*
+  CreateFileHandleQueue(FileHandle* aFileHandle);
+
+  FileHandleQueue*
+  GetFileHandleQueue(FileHandle* aFileHandle);
+
+  void
+  RemoveFileHandleQueue(FileHandle* aFileHandle);
+
+  bool
+  HasRunningFileHandles()
+  {
+    return !mFileHandleQueues.IsEmpty();
+  }
+
+  DelayedEnqueueInfo*
+  CreateDelayedEnqueueInfo(FileHandle* aFileHandle,
+                           FileHandleOp* aFileHandleOp,
+                           bool aFinish);
+
+  void
+  LockFileForReading(const nsAString& aFileName)
+  {
+    mFilesReading.PutEntry(aFileName);
+  }
+
+  void
+  LockFileForWriting(const nsAString& aFileName)
+  {
+    mFilesWriting.PutEntry(aFileName);
+  }
+
+  bool
+  IsFileLockedForReading(const nsAString& aFileName)
+  {
+    return mFilesReading.Contains(aFileName);
+  }
+
+  bool
+  IsFileLockedForWriting(const nsAString& aFileName)
+  {
+    return mFilesWriting.Contains(aFileName);
+  }
+
+private:
+  explicit DirectoryInfo(FileHandleThreadPool* aFileHandleThreadPool)
+    : mOwningFileHandleThreadPool(aFileHandleThreadPool)
+  { }
+};
+
+struct FileHandleThreadPool::StoragesCompleteCallback final
+{
+  friend class nsAutoPtr<StoragesCompleteCallback>;
+
+  nsTArray<nsCString> mDirectoryIds;
+  nsCOMPtr<nsIRunnable> mCallback;
+
+  StoragesCompleteCallback(nsTArray<nsCString>&& aDatabaseIds,
+                           nsIRunnable* aCallback);
+
+private:
+  ~StoragesCompleteCallback();
+};
+
+/******************************************************************************
+ * Actor class declarations
+ ******************************************************************************/
+
+class FileHandle
+  : public PBackgroundFileHandleParent
+{
+  friend class BackgroundMutableFileParentBase;
+
+  class FinishOp;
+
+  nsRefPtr<BackgroundMutableFileParentBase> mMutableFile;
+  nsCOMPtr<nsISupports> mStream;
+  uint64_t mActiveRequestCount;
+  FileHandleStorage mStorage;
+  Atomic<bool> mInvalidatedOnAnyThread;
+  FileMode mMode;
+  bool mHasBeenActive;
+  bool mActorDestroyed;
+  bool mInvalidated;
+  bool mAborted;
+  bool mFinishOrAbortReceived;
+  bool mFinishedOrAborted;
+  bool mForceAborted;
+
+  DEBUGONLY(nsCOMPtr<nsIEventTarget> mThreadPoolEventTarget;)
+
+public:
+  void
+  AssertIsOnThreadPool() const;
+
+  bool
+  IsActorDestroyed() const
+  {
+    AssertIsOnBackgroundThread();
+
+    return mActorDestroyed;
+  }
+
+  // Must be called on the background thread.
+  bool
+  IsInvalidated() const
+  {
+    MOZ_ASSERT(IsOnBackgroundThread(), "Use IsInvalidatedOnAnyThread()");
+    MOZ_ASSERT_IF(mInvalidated, mAborted);
+
+    return mInvalidated;
+  }
+
+  // May be called on any thread, but is more expensive than IsInvalidated().
+  bool
+  IsInvalidatedOnAnyThread() const
+  {
+    return mInvalidatedOnAnyThread;
+  }
+
+  void
+  SetActive()
+  {
+    AssertIsOnBackgroundThread();
+
+    mHasBeenActive = true;
+  }
+
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(mozilla::dom::FileHandle)
+
+  nsresult
+  GetOrCreateStream(nsISupports** aStream);
+
+  void
+  Abort(bool aForce);
+
+  FileHandleStorage
+  Storage() const
+  {
+    return mStorage;
+  }
+
+  FileMode
+  Mode() const
+  {
+    return mMode;
+  }
+
+  BackgroundMutableFileParentBase*
+  GetMutableFile() const
+  {
+    AssertIsOnBackgroundThread();
+    MOZ_ASSERT(mMutableFile);
+
+    return mMutableFile;
+  }
+
+  bool
+  IsAborted() const
+  {
+    AssertIsOnBackgroundThread();
+
+    return mAborted;
+  }
+
+  PBackgroundParent*
+  GetBackgroundParent() const
+  {
+    AssertIsOnBackgroundThread();
+    MOZ_ASSERT(!IsActorDestroyed());
+
+    return GetMutableFile()->GetBackgroundParent();
+  }
+
+  void
+  NoteActiveRequest();
+
+  void
+  NoteFinishedRequest();
+
+  void
+  Invalidate();
+
+private:
+  // This constructor is only called by BackgroundMutableFileParentBase.
+  FileHandle(BackgroundMutableFileParentBase* aMutableFile,
+             FileMode aMode);
+
+  // Reference counted.
+  ~FileHandle();
+
+  void
+  MaybeFinishOrAbort()
+  {
+    AssertIsOnBackgroundThread();
+
+    // If we've already finished or aborted then there's nothing else to do.
+    if (mFinishedOrAborted) {
+      return;
+    }
+
+    // If there are active requests then we have to wait for those requests to
+    // complete (see NoteFinishedRequest).
+    if (mActiveRequestCount) {
+      return;
+    }
+
+    // If we haven't yet received a finish or abort message then there could be
+    // additional requests coming so we should wait unless we're being forced to
+    // abort.
+    if (!mFinishOrAbortReceived && !mForceAborted) {
+      return;
+    }
+
+    FinishOrAbort();
+  }
+
+  void
+  SendCompleteNotification(bool aAborted);
+
+  bool
+  VerifyRequestParams(const FileRequestParams& aParams) const;
+
+  bool
+  VerifyRequestData(const FileRequestData& aData) const;
+
+  void
+  FinishOrAbort();
+
+  // IPDL methods are only called by IPDL.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+
+  virtual bool
+  RecvDeleteMe() override;
+
+  virtual bool
+  RecvFinish() override;
+
+  virtual bool
+  RecvAbort() override;
+
+  virtual PBackgroundFileRequestParent*
+  AllocPBackgroundFileRequestParent(const FileRequestParams& aParams) override;
+
+  virtual bool
+  RecvPBackgroundFileRequestConstructor(PBackgroundFileRequestParent* aActor,
+                                        const FileRequestParams& aParams)
+                                        override;
+
+  virtual bool
+  DeallocPBackgroundFileRequestParent(PBackgroundFileRequestParent* aActor)
+                                      override;
+};
+
+class FileHandleOp
+{
+protected:
+  nsCOMPtr<nsIEventTarget> mOwningThread;
+  nsRefPtr<FileHandle> mFileHandle;
+
+public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(FileHandleOp)
+
+  void
+  AssertIsOnOwningThread() const
+  {
+    AssertIsOnBackgroundThread();
+    MOZ_ASSERT(mOwningThread);
+    DebugOnly<bool> current;
+    MOZ_ASSERT(NS_SUCCEEDED(mOwningThread->IsOnCurrentThread(&current)));
+    MOZ_ASSERT(current);
+  }
+
+  nsIEventTarget*
+  OwningThread() const
+  {
+    return mOwningThread;
+  }
+
+  void
+  AssertIsOnThreadPool() const
+  {
+    MOZ_ASSERT(mFileHandle);
+    mFileHandle->AssertIsOnThreadPool();
+  }
+
+  void
+  Enqueue();
+
+  virtual void
+  RunOnThreadPool() = 0;
+
+  virtual void
+  RunOnOwningThread() = 0;
+
+protected:
+  FileHandleOp(FileHandle* aFileHandle)
+    : mOwningThread(NS_GetCurrentThread())
+    , mFileHandle(aFileHandle)
+  {
+    AssertIsOnOwningThread();
+    MOZ_ASSERT(aFileHandle);
+  }
+
+  virtual
+  ~FileHandleOp()
+  { }
+};
+
+class FileHandle::FinishOp
+  : public FileHandleOp
+{
+  friend class FileHandle;
+
+  bool mAborted;
+
+private:
+  FinishOp(FileHandle* aFileHandle,
+           bool aAborted)
+    : FileHandleOp(aFileHandle)
+    , mAborted(aAborted)
+  {
+    MOZ_ASSERT(aFileHandle);
+  }
+
+  ~FinishOp()
+  { }
+
+  virtual void
+  RunOnThreadPool() override;
+
+  virtual void
+  RunOnOwningThread() override;
+};
+
+class NormalFileHandleOp
+  : public FileHandleOp
+  , public PBackgroundFileRequestParent
+{
+  nsresult mResultCode;
+  Atomic<bool> mOperationMayProceed;
+  bool mActorDestroyed;
+  const bool mFileHandleIsAborted;
+
+  DEBUGONLY(bool mResponseSent;)
+
+protected:
+  nsCOMPtr<nsISupports> mFileStream;
+
+public:
+  void
+  NoteActorDestroyed()
+  {
+    AssertIsOnOwningThread();
+
+    mActorDestroyed = true;
+    mOperationMayProceed = false;
+  }
+
+  bool
+  IsActorDestroyed() const
+  {
+    AssertIsOnOwningThread();
+
+    return mActorDestroyed;
+  }
+
+  // May be called on any thread, but you should call IsActorDestroyed() if
+  // you know you're on the background thread because it is slightly faster.
+  bool
+  OperationMayProceed() const
+  {
+    return mOperationMayProceed;
+  }
+
+  // May be overridden by subclasses if they need to perform work on the
+  // background thread before being enqueued. Returning false will kill the
+  // child actors and prevent enqueue.
+  virtual bool
+  Init(FileHandle* aFileHandle);
+
+  // This callback will be called on the background thread before releasing the
+  // final reference to this request object. Subclasses may perform any
+  // additional cleanup here but must always call the base class implementation.
+  virtual void
+  Cleanup();
+
+protected:
+  NormalFileHandleOp(FileHandle* aFileHandle)
+    : FileHandleOp(aFileHandle)
+    , mResultCode(NS_OK)
+    , mOperationMayProceed(true)
+    , mActorDestroyed(false)
+    , mFileHandleIsAborted(aFileHandle->IsAborted())
+    DEBUGONLY(, mResponseSent(false))
+  {
+    MOZ_ASSERT(aFileHandle);
+  }
+
+  virtual
+  ~NormalFileHandleOp();
+
+  // Must be overridden in subclasses. Called on the target thread to allow the
+  // subclass to perform necessary file operations. A successful return value
+  // will trigger a SendSuccessResult callback on the background thread while
+  // a failure value will trigger a SendFailureResult callback.
+  virtual nsresult
+  DoFileWork(FileHandle* aFileHandle) = 0;
+
+  // Subclasses use this override to set the IPDL response value.
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) = 0;
+
+private:
+  nsresult
+  SendSuccessResult();
+
+  bool
+  SendFailureResult(nsresult aResultCode);
+
+  virtual void
+  RunOnThreadPool() override;
+
+  virtual void
+  RunOnOwningThread() override;
+
+  // IPDL methods.
+  virtual void
+  ActorDestroy(ActorDestroyReason aWhy) override;
+};
+
+class CopyFileHandleOp
+  : public NormalFileHandleOp
+{
+  class ProgressRunnable;
+
+protected:
+  nsCOMPtr<nsISupports> mBufferStream;
+
+  uint64_t mOffset;
+  uint64_t mSize;
+
+  bool mRead;
+
+protected:
+  CopyFileHandleOp(FileHandle* aFileHandle)
+    : NormalFileHandleOp(aFileHandle)
+    , mOffset(0)
+    , mSize(0)
+    , mRead(true)
+  { }
+
+  virtual nsresult
+  DoFileWork(FileHandle* aFileHandle) override;
+
+  virtual void
+  Cleanup() override;
+};
+
+class CopyFileHandleOp::ProgressRunnable final
+  : public nsRunnable
+{
+  nsRefPtr<CopyFileHandleOp> mCopyFileHandleOp;
+  uint64_t mProgress;
+  uint64_t mProgressMax;
+
+public:
+  ProgressRunnable(CopyFileHandleOp* aCopyFileHandleOp,
+                   uint64_t aProgress,
+                   uint64_t aProgressMax)
+    : mCopyFileHandleOp(aCopyFileHandleOp)
+    , mProgress(aProgress)
+    , mProgressMax(aProgressMax)
+  { }
+
+private:
+  ~ProgressRunnable() {}
+
+  NS_DECL_NSIRUNNABLE
+};
+
+class GetMetadataOp
+  : public NormalFileHandleOp
+{
+  friend class FileHandle;
+
+  const FileRequestGetMetadataParams mParams;
+
+protected:
+  FileRequestMetadata mMetadata;
+
+protected:
+  // Only created by FileHandle.
+  GetMetadataOp(FileHandle* aFileHandle,
+                const FileRequestParams& aParams);
+
+  ~GetMetadataOp()
+  { }
+
+  virtual nsresult
+  DoFileWork(FileHandle* aFileHandle) override;
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+class ReadOp final
+  : public CopyFileHandleOp
+{
+  friend class FileHandle;
+
+  class MemoryOutputStream;
+
+  const FileRequestReadParams mParams;
+
+private:
+  // Only created by FileHandle.
+  ReadOp(FileHandle* aFileHandle,
+         const FileRequestParams& aParams);
+
+  ~ReadOp()
+  { }
+
+  virtual bool
+  Init(FileHandle* aFileHandle) override;
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+class ReadOp::MemoryOutputStream final
+  : public nsIOutputStream
+{
+  nsCString mData;
+  uint64_t mOffset;
+
+public:
+  static already_AddRefed<MemoryOutputStream>
+  Create(uint64_t aSize);
+
+  const nsCString&
+  Data() const
+  {
+    return mData;
+  }
+
+private:
+  MemoryOutputStream()
+  : mOffset(0)
+  { }
+
+  virtual ~MemoryOutputStream()
+  { }
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIOUTPUTSTREAM
+};
+
+class WriteOp final
+  : public CopyFileHandleOp
+{
+  friend class FileHandle;
+
+  const FileRequestWriteParams mParams;
+
+private:
+  // Only created by FileHandle.
+  WriteOp(FileHandle* aFileHandle,
+          const FileRequestParams& aParams);
+
+  ~WriteOp()
+  { }
+
+  virtual bool
+  Init(FileHandle* aFileHandle) override;
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+class TruncateOp final
+  : public NormalFileHandleOp
+{
+  friend class FileHandle;
+
+  const FileRequestTruncateParams mParams;
+
+private:
+  // Only created by FileHandle.
+  TruncateOp(FileHandle* aFileHandle,
+                        const FileRequestParams& aParams);
+
+  ~TruncateOp()
+  { }
+
+  virtual nsresult
+  DoFileWork(FileHandle* aFileHandle) override;
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+class FlushOp final
+  : public NormalFileHandleOp
+{
+  friend class FileHandle;
+
+  const FileRequestFlushParams mParams;
+
+private:
+  // Only created by FileHandle.
+  FlushOp(FileHandle* aFileHandle,
+          const FileRequestParams& aParams);
+
+  ~FlushOp()
+  { }
+
+  virtual nsresult
+  DoFileWork(FileHandle* aFileHandle) override;
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+class GetFileOp final
+  : public GetMetadataOp
+{
+  friend class FileHandle;
+
+  PBackgroundParent* mBackgroundParent;
+
+private:
+  // Only created by FileHandle.
+  GetFileOp(FileHandle* aFileHandle,
+            const FileRequestParams& aParams);
+
+  ~GetFileOp()
+  { }
+
+  virtual void
+  GetResponse(FileRequestResponse& aResponse) override;
+};
+
+namespace {
+
+/*******************************************************************************
+ * Helper Functions
+ ******************************************************************************/
+
+FileHandleThreadPool*
+GetFileHandleThreadPoolFor(FileHandleStorage aStorage)
+{
+  switch (aStorage) {
+    case FILE_HANDLE_STORAGE_IDB:
+      return mozilla::dom::indexedDB::GetFileHandleThreadPool();
+
+    default:
+      MOZ_CRASH("Bad file handle storage value!");
+  }
+}
+
+} // namespace
+
+/*******************************************************************************
+ * FileHandleThreadPool implementation
+ ******************************************************************************/
+
+FileHandleThreadPool::FileHandleThreadPool()
+  : mOwningThread(NS_GetCurrentThread())
+  , mShutdownRequested(false)
+  , mShutdownComplete(false)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mOwningThread);
+  AssertIsOnOwningThread();
+}
+
+FileHandleThreadPool::~FileHandleThreadPool()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mDirectoryInfos.Count());
+  MOZ_ASSERT(mCompleteCallbacks.IsEmpty());
+  MOZ_ASSERT(mShutdownRequested);
+  MOZ_ASSERT(mShutdownComplete);
+}
+
+// static
+already_AddRefed<FileHandleThreadPool>
+FileHandleThreadPool::Create()
+{
+  AssertIsOnBackgroundThread();
+
+  nsRefPtr<FileHandleThreadPool> fileHandleThreadPool =
+    new FileHandleThreadPool();
+  fileHandleThreadPool->AssertIsOnOwningThread();
+
+  if (NS_WARN_IF(NS_FAILED(fileHandleThreadPool->Init()))) {
+    return nullptr;
+  }
+
+  return fileHandleThreadPool.forget();
+}
+
+#ifdef DEBUG
+
+void
+FileHandleThreadPool::AssertIsOnOwningThread() const
+{
+  MOZ_ASSERT(mOwningThread);
+
+  bool current;
+  MOZ_ALWAYS_TRUE(NS_SUCCEEDED(mOwningThread->IsOnCurrentThread(&current)));
+  MOZ_ASSERT(current);
+}
+
+nsIEventTarget*
+FileHandleThreadPool::GetThreadPoolEventTarget() const
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mThreadPool);
+
+  return mThreadPool;
+}
+
+#endif // DEBUG
+
+void
+FileHandleThreadPool::Enqueue(FileHandle* aFileHandle,
+                              FileHandleOp* aFileHandleOp,
+                              bool aFinish)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+  MOZ_ASSERT(!mShutdownRequested);
+
+  BackgroundMutableFileParentBase* mutableFile = aFileHandle->GetMutableFile();
+
+  const nsACString& directoryId = mutableFile->DirectoryId();
+  const nsAString& fileName = mutableFile->FileName();
+  bool modeIsWrite = aFileHandle->Mode() == FileMode::Readwrite;
+
+  DirectoryInfo* directoryInfo;
+  if (!mDirectoryInfos.Get(directoryId, &directoryInfo)) {
+    nsAutoPtr<DirectoryInfo> newDirectoryInfo(new DirectoryInfo(this));
+
+    mDirectoryInfos.Put(directoryId, newDirectoryInfo);
+
+    directoryInfo = newDirectoryInfo.forget();
+  }
+
+  FileHandleQueue* existingFileHandleQueue =
+    directoryInfo->GetFileHandleQueue(aFileHandle);
+
+  if (existingFileHandleQueue) {
+    existingFileHandleQueue->Enqueue(aFileHandleOp);
+    if (aFinish) {
+      existingFileHandleQueue->Finish();
+    }
+    return;
+  }
+
+  bool lockedForReading = directoryInfo->IsFileLockedForReading(fileName);
+  bool lockedForWriting = directoryInfo->IsFileLockedForWriting(fileName);
+
+  if (modeIsWrite) {
+    if (!lockedForWriting) {
+      directoryInfo->LockFileForWriting(fileName);
+    }
+  }
+  else {
+    if (!lockedForReading) {
+      directoryInfo->LockFileForReading(fileName);
+    }
+  }
+
+  if (lockedForWriting || (lockedForReading && modeIsWrite)) {
+    directoryInfo->CreateDelayedEnqueueInfo(aFileHandle,
+                                            aFileHandleOp,
+                                            aFinish);
+  }
+  else {
+    FileHandleQueue* fileHandleQueue =
+      directoryInfo->CreateFileHandleQueue(aFileHandle);
+
+    if (aFileHandleOp) {
+      fileHandleQueue->Enqueue(aFileHandleOp);
+      if (aFinish) {
+        existingFileHandleQueue->Finish();
+      }
+    }
+  }
+}
+
+void
+FileHandleThreadPool::WaitForDirectoriesToComplete(
+                                             nsTArray<nsCString>&& aDirectoryIds,
+                                             nsIRunnable* aCallback)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!aDirectoryIds.IsEmpty());
+  MOZ_ASSERT(aCallback);
+
+  nsAutoPtr<StoragesCompleteCallback> callback(
+    new StoragesCompleteCallback(Move(aDirectoryIds), aCallback));
+
+  if (!MaybeFireCallback(callback)) {
+    mCompleteCallbacks.AppendElement(callback.forget());
+  }
+}
+
+void
+FileHandleThreadPool::Shutdown()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(!mShutdownRequested);
+  MOZ_ASSERT(!mShutdownComplete);
+
+  mShutdownRequested = true;
+
+  if (!mThreadPool) {
+    MOZ_ASSERT(!mDirectoryInfos.Count());
+    MOZ_ASSERT(mCompleteCallbacks.IsEmpty());
+
+    mShutdownComplete = true;
+    return;
+  }
+
+  if (!mDirectoryInfos.Count()) {
+    Cleanup();
+
+    MOZ_ASSERT(mShutdownComplete);
+    return;
+  }
+
+  nsIThread* currentThread = NS_GetCurrentThread();
+  MOZ_ASSERT(currentThread);
+
+  while (!mShutdownComplete) {
+    MOZ_ALWAYS_TRUE(NS_ProcessNextEvent(currentThread));
+  }
+}
+
+nsresult
+FileHandleThreadPool::Init()
+{
+  AssertIsOnOwningThread();
+
+  mThreadPool = new nsThreadPool();
+
+  nsresult rv = mThreadPool->SetName(NS_LITERAL_CSTRING("FileHandles"));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = mThreadPool->SetThreadLimit(kThreadLimit);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = mThreadPool->SetIdleThreadLimit(kIdleThreadLimit);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = mThreadPool->SetIdleThreadTimeout(kIdleThreadTimeoutMs);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+void
+FileHandleThreadPool::Cleanup()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mThreadPool);
+  MOZ_ASSERT(mShutdownRequested);
+  MOZ_ASSERT(!mShutdownComplete);
+  MOZ_ASSERT(!mDirectoryInfos.Count());
+
+  MOZ_ALWAYS_TRUE(NS_SUCCEEDED(mThreadPool->Shutdown()));
+
+  if (!mCompleteCallbacks.IsEmpty()) {
+    // Run all callbacks manually now.
+    for (uint32_t count = mCompleteCallbacks.Length(), index = 0;
+         index < count;
+         index++) {
+      nsAutoPtr<StoragesCompleteCallback> completeCallback(
+        mCompleteCallbacks[index].forget());
+      MOZ_ASSERT(completeCallback);
+      MOZ_ASSERT(completeCallback->mCallback);
+
+      unused << completeCallback->mCallback->Run();
+    }
+
+    mCompleteCallbacks.Clear();
+
+    // And make sure they get processed.
+    nsIThread* currentThread = NS_GetCurrentThread();
+    MOZ_ASSERT(currentThread);
+
+    MOZ_ALWAYS_TRUE(NS_SUCCEEDED(NS_ProcessPendingEvents(currentThread)));
+  }
+
+  mShutdownComplete = true;
+}
+
+void
+FileHandleThreadPool::FinishFileHandle(FileHandle* aFileHandle)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+
+  BackgroundMutableFileParentBase* mutableFile = aFileHandle->GetMutableFile();
+  const nsACString& directoryId = mutableFile->DirectoryId();
+
+  DirectoryInfo* directoryInfo;
+  if (!mDirectoryInfos.Get(directoryId, &directoryInfo)) {
+    NS_ERROR("We don't know anyting about this directory?!");
+    return;
+  }
+
+  directoryInfo->RemoveFileHandleQueue(aFileHandle);
+
+  if (!directoryInfo->HasRunningFileHandles()) {
+    mDirectoryInfos.Remove(directoryId);
+
+    // See if we need to fire any complete callbacks.
+    uint32_t index = 0;
+    while (index < mCompleteCallbacks.Length()) {
+      if (MaybeFireCallback(mCompleteCallbacks[index])) {
+        mCompleteCallbacks.RemoveElementAt(index);
+      }
+      else {
+        index++;
+      }
+    }
+
+    if (mShutdownRequested && !mDirectoryInfos.Count()) {
+      Cleanup();
+    }
+  }
+}
+
+bool
+FileHandleThreadPool::MaybeFireCallback(StoragesCompleteCallback* aCallback)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aCallback);
+  MOZ_ASSERT(!aCallback->mDirectoryIds.IsEmpty());
+  MOZ_ASSERT(aCallback->mCallback);
+
+  for (uint32_t count = aCallback->mDirectoryIds.Length(), index = 0;
+       index < count;
+       index++) {
+    const nsCString& directoryId = aCallback->mDirectoryIds[index];
+    MOZ_ASSERT(!directoryId.IsEmpty());
+
+    if (mDirectoryInfos.Get(directoryId, nullptr)) {
+      return false;
+    }
+  }
+
+  aCallback->mCallback->Run();
+  return true;
+}
+
+FileHandleThreadPool::
+FileHandleQueue::FileHandleQueue(FileHandleThreadPool* aFileHandleThreadPool,
+                                 FileHandle* aFileHandle)
+  : mOwningFileHandleThreadPool(aFileHandleThreadPool)
+  , mFileHandle(aFileHandle)
+  , mShouldFinish(false)
+{
+  MOZ_ASSERT(aFileHandleThreadPool);
+  aFileHandleThreadPool->AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+}
+
+void
+FileHandleThreadPool::
+FileHandleQueue::Enqueue(FileHandleOp* aFileHandleOp)
+{
+  MOZ_ASSERT(!mShouldFinish, "Enqueue called after Finish!");
+
+  mQueue.AppendElement(aFileHandleOp);
+
+  ProcessQueue();
+}
+
+void
+FileHandleThreadPool::
+FileHandleQueue::Finish()
+{
+  MOZ_ASSERT(!mShouldFinish, "Finish called more than once!");
+
+  mShouldFinish = true;
+}
+
+void
+FileHandleThreadPool::
+FileHandleQueue::ProcessQueue()
+{
+  if (mCurrentOp) {
+    return;
+  }
+
+  if (mQueue.IsEmpty()) {
+    if (mShouldFinish) {
+      mOwningFileHandleThreadPool->FinishFileHandle(mFileHandle);
+
+      // Make sure this is released on this thread.
+      mOwningFileHandleThreadPool = nullptr;
+    }
+
+    return;
+  }
+
+  mCurrentOp = mQueue[0];
+  mQueue.RemoveElementAt(0);
+
+  nsCOMPtr<nsIThreadPool> threadPool = mOwningFileHandleThreadPool->mThreadPool;
+  MOZ_ASSERT(threadPool);
+
+  MOZ_ALWAYS_TRUE(NS_SUCCEEDED(threadPool->Dispatch(this, NS_DISPATCH_NORMAL)));
+}
+
+NS_IMETHODIMP
+FileHandleThreadPool::
+FileHandleQueue::Run()
+{
+  MOZ_ASSERT(mCurrentOp);
+
+  if (IsOnBackgroundThread()) {
+    nsRefPtr<FileHandleOp> currentOp;
+
+    mCurrentOp.swap(currentOp);
+    ProcessQueue();
+
+    currentOp->RunOnOwningThread();
+  } else {
+    mCurrentOp->RunOnThreadPool();
+
+    nsCOMPtr<nsIEventTarget> backgroundThread = mCurrentOp->OwningThread();
+
+    MOZ_ALWAYS_TRUE(NS_SUCCEEDED(
+      backgroundThread->Dispatch(this, NS_DISPATCH_NORMAL)));
+  }
+
+  return NS_OK;
+}
+
+auto
+FileHandleThreadPool::
+DirectoryInfo::CreateFileHandleQueue(FileHandle* aFileHandle)
+  -> FileHandleQueue*
+{
+  nsRefPtr<FileHandleQueue>* fileHandleQueue =
+    mFileHandleQueues.AppendElement();
+  *fileHandleQueue = new FileHandleQueue(mOwningFileHandleThreadPool,
+                                         aFileHandle);
+  return fileHandleQueue->get();
+}
+
+auto
+FileHandleThreadPool::
+DirectoryInfo::GetFileHandleQueue(FileHandle* aFileHandle) -> FileHandleQueue*
+{
+  uint32_t count = mFileHandleQueues.Length();
+  for (uint32_t index = 0; index < count; index++) {
+    nsRefPtr<FileHandleQueue>& fileHandleQueue = mFileHandleQueues[index];
+    if (fileHandleQueue->mFileHandle == aFileHandle) {
+      return fileHandleQueue;
+    }
+  }
+  return nullptr;
+}
+
+void
+FileHandleThreadPool::
+DirectoryInfo::RemoveFileHandleQueue(FileHandle* aFileHandle)
+{
+  for (uint32_t index = 0; index < mDelayedEnqueueInfos.Length(); index++) {
+    if (mDelayedEnqueueInfos[index].mFileHandle == aFileHandle) {
+      MOZ_ASSERT(!mDelayedEnqueueInfos[index].mFileHandleOp, "Should be null!");
+      mDelayedEnqueueInfos.RemoveElementAt(index);
+      return;
+    }
+  }
+
+  uint32_t fileHandleCount = mFileHandleQueues.Length();
+
+  // We can't just remove entries from lock hash tables, we have to rebuild
+  // them instead. Multiple FileHandle objects may lock the same file
+  // (one entry can represent multiple locks).
+
+  mFilesReading.Clear();
+  mFilesWriting.Clear();
+
+  for (uint32_t index = 0, count = fileHandleCount; index < count; index++) {
+    FileHandle* fileHandle = mFileHandleQueues[index]->mFileHandle;
+    if (fileHandle == aFileHandle) {
+      MOZ_ASSERT(count == fileHandleCount, "More than one match?!");
+
+      mFileHandleQueues.RemoveElementAt(index);
+      index--;
+      count--;
+
+      continue;
+    }
+
+    const nsAString& fileName = fileHandle->GetMutableFile()->FileName();
+
+    if (fileHandle->Mode() == FileMode::Readwrite) {
+      if (!IsFileLockedForWriting(fileName)) {
+        LockFileForWriting(fileName);
+      }
+    }
+    else {
+      if (!IsFileLockedForReading(fileName)) {
+        LockFileForReading(fileName);
+      }
+    }
+  }
+
+  MOZ_ASSERT(mFileHandleQueues.Length() == fileHandleCount - 1,
+             "Didn't find the file handle we were looking for!");
+
+  nsTArray<DelayedEnqueueInfo> delayedEnqueueInfos;
+  delayedEnqueueInfos.SwapElements(mDelayedEnqueueInfos);
+
+  for (uint32_t index = 0; index < delayedEnqueueInfos.Length(); index++) {
+    DelayedEnqueueInfo& delayedEnqueueInfo = delayedEnqueueInfos[index];
+    mOwningFileHandleThreadPool->Enqueue(delayedEnqueueInfo.mFileHandle,
+                                         delayedEnqueueInfo.mFileHandleOp,
+                                         delayedEnqueueInfo.mFinish);
+  }
+}
+
+auto
+FileHandleThreadPool::
+DirectoryInfo::CreateDelayedEnqueueInfo(FileHandle* aFileHandle,
+                                        FileHandleOp* aFileHandleOp,
+                                        bool aFinish) -> DelayedEnqueueInfo*
+{
+  DelayedEnqueueInfo* info = mDelayedEnqueueInfos.AppendElement();
+  info->mFileHandle = aFileHandle;
+  info->mFileHandleOp = aFileHandleOp;
+  info->mFinish = aFinish;
+  return info;
+}
+
+FileHandleThreadPool::
+StoragesCompleteCallback::StoragesCompleteCallback(
+                                             nsTArray<nsCString>&& aDirectoryIds,
+                                             nsIRunnable* aCallback)
+  : mDirectoryIds(Move(aDirectoryIds))
+  , mCallback(aCallback)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mDirectoryIds.IsEmpty());
+  MOZ_ASSERT(aCallback);
+
+  MOZ_COUNT_CTOR(FileHandleThreadPool::StoragesCompleteCallback);
+}
+
+FileHandleThreadPool::
+StoragesCompleteCallback::~StoragesCompleteCallback()
+{
+  AssertIsOnBackgroundThread();
+
+  MOZ_COUNT_DTOR(FileHandleThreadPool::StoragesCompleteCallback);
+}
+
+/*******************************************************************************
+ * BackgroundMutableFileParentBase
+ ******************************************************************************/
+
+BackgroundMutableFileParentBase::BackgroundMutableFileParentBase(
+                                                 FileHandleStorage aStorage,
+                                                 const nsACString& aDirectoryId,
+                                                 const nsAString& aFileName,
+                                                 nsIFile* aFile)
+  : mDirectoryId(aDirectoryId)
+  , mFileName(aFileName)
+  , mStorage(aStorage)
+  , mInvalidated(false)
+  , mActorWasAlive(false)
+  , mActorDestroyed(false)
+  , mFile(aFile)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aStorage != FILE_HANDLE_STORAGE_MAX);
+  MOZ_ASSERT(!aDirectoryId.IsEmpty());
+  MOZ_ASSERT(!aFileName.IsEmpty());
+  MOZ_ASSERT(aFile);
+}
+
+BackgroundMutableFileParentBase::~BackgroundMutableFileParentBase()
+{
+  MOZ_ASSERT_IF(mActorWasAlive, mActorDestroyed);
+}
+
+void
+BackgroundMutableFileParentBase::Invalidate()
+{
+  AssertIsOnBackgroundThread();
+
+  class MOZ_STACK_CLASS Helper final
+  {
+  public:
+    static bool
+    InvalidateFileHandles(nsTHashtable<nsPtrHashKey<FileHandle>>& aTable)
+    {
+      AssertIsOnBackgroundThread();
+
+      const uint32_t count = aTable.Count();
+      if (!count) {
+        return true;
+      }
+
+      FallibleTArray<nsRefPtr<FileHandle>> fileHandles;
+      if (NS_WARN_IF(!fileHandles.SetCapacity(count, fallible))) {
+        return false;
+      }
+
+      for (auto iter = aTable.Iter(); !iter.Done(); iter.Next()) {
+        if (NS_WARN_IF(!fileHandles.AppendElement(iter.Get()->GetKey(),
+                                                  fallible))) {
+          return false;
+        }
+      }
+
+      if (count) {
+        for (uint32_t index = 0; index < count; index++) {
+          nsRefPtr<FileHandle> fileHandle = fileHandles[index].forget();
+          MOZ_ASSERT(fileHandle);
+
+          fileHandle->Invalidate();
+        }
+      }
+
+      return true;
+    }
+  };
+
+  if (mInvalidated) {
+    return;
+  }
+
+  mInvalidated = true;
+
+  if (!Helper::InvalidateFileHandles(mFileHandles)) {
+    NS_WARNING("Failed to abort all file handles!");
+  }
+}
+
+bool
+BackgroundMutableFileParentBase::RegisterFileHandle(FileHandle* aFileHandle)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aFileHandle);
+  MOZ_ASSERT(!mFileHandles.GetEntry(aFileHandle));
+  MOZ_ASSERT(!mInvalidated);
+
+  if (NS_WARN_IF(!mFileHandles.PutEntry(aFileHandle, fallible))) {
+    return false;
+  }
+
+  if (mFileHandles.Count() == 1) {
+    NoteActiveState();
+  }
+
+  return true;
+}
+
+void
+BackgroundMutableFileParentBase::UnregisterFileHandle(FileHandle* aFileHandle)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aFileHandle);
+  MOZ_ASSERT(mFileHandles.GetEntry(aFileHandle));
+
+  mFileHandles.RemoveEntry(aFileHandle);
+
+  if (!mFileHandles.Count()) {
+    NoteInactiveState();
+  }
+}
+
+void
+BackgroundMutableFileParentBase::SetActorAlive()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorWasAlive);
+  MOZ_ASSERT(!mActorDestroyed);
+
+  mActorWasAlive = true;
+
+  // This reference will be absorbed by IPDL and released when the actor is
+  // destroyed.
+  AddRef();
+}
+
+already_AddRefed<nsISupports>
+BackgroundMutableFileParentBase::CreateStream(bool aReadOnly)
+{
+  AssertIsOnBackgroundThread();
+
+  nsresult rv;
+
+  if (aReadOnly) {
+    nsCOMPtr<nsIInputStream> stream;
+    rv = NS_NewLocalFileInputStream(getter_AddRefs(stream), mFile, -1, -1,
+                                    nsIFileInputStream::DEFER_OPEN);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return nullptr;
+    }
+    return stream.forget();
+  }
+
+  nsCOMPtr<nsIFileStream> stream;
+  rv = NS_NewLocalFileStream(getter_AddRefs(stream), mFile, -1, -1,
+                             nsIFileStream::DEFER_OPEN);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return nullptr;
+  }
+  return stream.forget();
+}
+
+void
+BackgroundMutableFileParentBase::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  mActorDestroyed = true;
+
+  if (!IsInvalidated()) {
+    Invalidate();
+  }
+}
+
+PBackgroundFileHandleParent*
+BackgroundMutableFileParentBase::AllocPBackgroundFileHandleParent(
+                                                          const FileMode& aMode)
+{
+  AssertIsOnBackgroundThread();
+
+  if (NS_WARN_IF(aMode != FileMode::Readonly &&
+                 aMode != FileMode::Readwrite)) {
+    ASSERT_UNLESS_FUZZING();
+    return nullptr;
+  }
+
+  nsRefPtr<FileHandle> fileHandle = new FileHandle(this, aMode);
+
+  return fileHandle.forget().take();
+}
+
+bool
+BackgroundMutableFileParentBase::RecvPBackgroundFileHandleConstructor(
+                                            PBackgroundFileHandleParent* aActor,
+                                            const FileMode& aMode)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(aMode == FileMode::Readonly || aMode == FileMode::Readwrite);
+
+  FileHandleThreadPool* fileHandleThreadPool =
+    GetFileHandleThreadPoolFor(mStorage);
+  MOZ_ASSERT(fileHandleThreadPool);
+
+  auto* fileHandle = static_cast<FileHandle*>(aActor);
+
+  // Add a placeholder for this file handle immediately.
+  fileHandleThreadPool->Enqueue(fileHandle, nullptr, false);
+
+  fileHandle->SetActive();
+
+  if (NS_WARN_IF(!RegisterFileHandle(fileHandle))) {
+    fileHandle->Abort(/* aForce */ false);
+    return true;
+  }
+
+  return true;
+}
+
+bool
+BackgroundMutableFileParentBase::DeallocPBackgroundFileHandleParent(
+                                            PBackgroundFileHandleParent* aActor)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  nsRefPtr<FileHandle> fileHandle =
+    dont_AddRef(static_cast<FileHandle*>(aActor));
+  return true;
+}
+
+bool
+BackgroundMutableFileParentBase::RecvDeleteMe()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActorDestroyed);
+
+  return PBackgroundMutableFileParent::Send__delete__(this);
+}
+
+bool
+BackgroundMutableFileParentBase::RecvGetFileId(int64_t* aFileId)
+{
+  AssertIsOnBackgroundThread();
+
+  *aFileId = -1;
+  return true;
+}
+
+/*******************************************************************************
+ * FileHandle
+ ******************************************************************************/
+
+FileHandle::FileHandle(BackgroundMutableFileParentBase* aMutableFile,
+                       FileMode aMode)
+  : mMutableFile(aMutableFile)
+  , mActiveRequestCount(0)
+  , mStorage(aMutableFile->Storage())
+  , mInvalidatedOnAnyThread(false)
+  , mMode(aMode)
+  , mHasBeenActive(false)
+  , mActorDestroyed(false)
+  , mInvalidated(false)
+  , mAborted(false)
+  , mFinishOrAbortReceived(false)
+  , mFinishedOrAborted(false)
+  , mForceAborted(false)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aMutableFile);
+
+#ifdef DEBUG
+  FileHandleThreadPool* fileHandleThreadPool =
+    GetFileHandleThreadPoolFor(mStorage);
+  MOZ_ASSERT(fileHandleThreadPool);
+
+  mThreadPoolEventTarget = fileHandleThreadPool->GetThreadPoolEventTarget();
+#endif
+}
+
+FileHandle::~FileHandle()
+{
+  MOZ_ASSERT(!mActiveRequestCount);
+  MOZ_ASSERT(mActorDestroyed);
+  MOZ_ASSERT_IF(mHasBeenActive, mFinishedOrAborted);
+}
+
+void
+FileHandle::AssertIsOnThreadPool() const
+{
+  MOZ_ASSERT(mThreadPoolEventTarget);
+  DebugOnly<bool> current;
+  MOZ_ASSERT(NS_SUCCEEDED(mThreadPoolEventTarget->IsOnCurrentThread(&current)));
+  MOZ_ASSERT(current);
+}
+
+nsresult
+FileHandle::GetOrCreateStream(nsISupports** aStream)
+{
+  AssertIsOnBackgroundThread();
+
+  if (!mStream) {
+    nsCOMPtr<nsISupports> stream =
+      mMutableFile->CreateStream(mMode == FileMode::Readonly);
+    if (NS_WARN_IF(!stream)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    stream.swap(mStream);
+  }
+
+  nsCOMPtr<nsISupports> stream(mStream);
+  stream.forget(aStream);
+
+  return NS_OK;
+}
+
+void
+FileHandle::Abort(bool aForce)
+{
+  AssertIsOnBackgroundThread();
+
+  mAborted = true;
+
+  if (aForce) {
+    mForceAborted = true;
+  }
+
+  MaybeFinishOrAbort();
+}
+
+void
+FileHandle::NoteActiveRequest()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mActiveRequestCount < UINT64_MAX);
+
+  mActiveRequestCount++;
+}
+
+void
+FileHandle::NoteFinishedRequest()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mActiveRequestCount);
+
+  mActiveRequestCount--;
+
+  MaybeFinishOrAbort();
+}
+
+void
+FileHandle::Invalidate()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mInvalidated == mInvalidatedOnAnyThread);
+
+  if (!mInvalidated) {
+    mInvalidated = true;
+    mInvalidatedOnAnyThread = true;
+
+    Abort(/* aForce */ true);
+  }
+}
+
+void
+FileHandle::SendCompleteNotification(bool aAborted)
+{
+  AssertIsOnBackgroundThread();
+
+  if (!IsActorDestroyed()) {
+    unused << SendComplete(aAborted);
+  }
+}
+
+bool
+FileHandle::VerifyRequestParams(const FileRequestParams& aParams) const
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aParams.type() != FileRequestParams::T__None);
+
+  switch (aParams.type()) {
+    case FileRequestParams::TFileRequestGetMetadataParams: {
+      const FileRequestGetMetadataParams& params =
+        aParams.get_FileRequestGetMetadataParams();
+
+      if (NS_WARN_IF(!params.size() && !params.lastModified())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestParams::TFileRequestReadParams: {
+      const FileRequestReadParams& params =
+        aParams.get_FileRequestReadParams();
+
+      if (NS_WARN_IF(params.offset() == UINT64_MAX)) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      if (NS_WARN_IF(!params.size())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestParams::TFileRequestWriteParams: {
+      if (NS_WARN_IF(mMode != FileMode::Readwrite)) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      const FileRequestWriteParams& params =
+        aParams.get_FileRequestWriteParams();
+
+
+      if (NS_WARN_IF(!params.dataLength())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      if (NS_WARN_IF(!VerifyRequestData(params.data()))) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestParams::TFileRequestTruncateParams: {
+      if (NS_WARN_IF(mMode != FileMode::Readwrite)) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      const FileRequestTruncateParams& params =
+        aParams.get_FileRequestTruncateParams();
+
+      if (NS_WARN_IF(params.offset() == UINT64_MAX)) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestParams::TFileRequestFlushParams: {
+      if (NS_WARN_IF(mMode != FileMode::Readwrite)) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestParams::TFileRequestGetFileParams: {
+      break;
+    }
+
+    default:
+      MOZ_CRASH("Should never get here!");
+  }
+
+  return true;
+}
+
+bool
+FileHandle::VerifyRequestData(const FileRequestData& aData) const
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aData.type() != FileRequestData::T__None);
+
+  switch (aData.type()) {
+    case FileRequestData::TFileRequestStringData: {
+      const FileRequestStringData& data =
+        aData.get_FileRequestStringData();
+
+      if (NS_WARN_IF(data.string().IsEmpty())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    case FileRequestData::TFileRequestBlobData: {
+      const FileRequestBlobData& data =
+        aData.get_FileRequestBlobData();
+
+      if (NS_WARN_IF(data.blobChild())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      if (NS_WARN_IF(!data.blobParent())) {
+        ASSERT_UNLESS_FUZZING();
+        return false;
+      }
+
+      break;
+    }
+
+    default:
+      MOZ_CRASH("Should never get here!");
+  }
+
+  return true;
+}
+
+void
+FileHandle::FinishOrAbort()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mFinishedOrAborted);
+
+  mFinishedOrAborted = true;
+
+  if (!mHasBeenActive) {
+    return;
+  }
+
+  nsRefPtr<FinishOp> finishOp = new FinishOp(this, mAborted);
+
+  FileHandleThreadPool* fileHandleThreadPool =
+    GetFileHandleThreadPoolFor(mStorage);
+  MOZ_ASSERT(fileHandleThreadPool);
+
+  fileHandleThreadPool->Enqueue(this, finishOp, true);
+}
+
+void
+FileHandle::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnBackgroundThread();
+
+  MOZ_ASSERT(!mActorDestroyed);
+
+  mActorDestroyed = true;
+
+  if (!mFinishedOrAborted) {
+    mAborted = true;
+
+    mForceAborted = true;
+
+    MaybeFinishOrAbort();
+  }
+}
+
+bool
+FileHandle::RecvDeleteMe()
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!IsActorDestroyed());
+
+  return PBackgroundFileHandleParent::Send__delete__(this);
+}
+
+bool
+FileHandle::RecvFinish()
+{
+  AssertIsOnBackgroundThread();
+
+  if (NS_WARN_IF(mFinishOrAbortReceived)) {
+    ASSERT_UNLESS_FUZZING();
+    return false;
+  }
+
+  mFinishOrAbortReceived = true;
+
+  MaybeFinishOrAbort();
+  return true;
+}
+
+bool
+FileHandle::RecvAbort()
+{
+  AssertIsOnBackgroundThread();
+
+  if (NS_WARN_IF(mFinishOrAbortReceived)) {
+    ASSERT_UNLESS_FUZZING();
+    return false;
+  }
+
+  mFinishOrAbortReceived = true;
+
+  Abort(/* aForce */ false);
+  return true;
+}
+
+PBackgroundFileRequestParent*
+FileHandle::AllocPBackgroundFileRequestParent(const FileRequestParams& aParams)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aParams.type() != FileRequestParams::T__None);
+
+#ifdef DEBUG
+  // Always verify parameters in DEBUG builds!
+  bool trustParams = false;
+#else
+  PBackgroundParent* backgroundActor = GetBackgroundParent();
+  MOZ_ASSERT(backgroundActor);
+
+  bool trustParams = !BackgroundParent::IsOtherProcessActor(backgroundActor);
+#endif
+
+  if (NS_WARN_IF(!trustParams && !VerifyRequestParams(aParams))) {
+    ASSERT_UNLESS_FUZZING();
+    return nullptr;
+  }
+
+  if (NS_WARN_IF(mFinishOrAbortReceived)) {
+    ASSERT_UNLESS_FUZZING();
+    return nullptr;
+  }
+
+  nsRefPtr<NormalFileHandleOp> actor;
+
+  switch (aParams.type()) {
+    case FileRequestParams::TFileRequestGetMetadataParams:
+      actor = new GetMetadataOp(this, aParams);
+      break;
+
+    case FileRequestParams::TFileRequestReadParams:
+      actor = new ReadOp(this, aParams);
+      break;
+
+    case FileRequestParams::TFileRequestWriteParams:
+      actor = new WriteOp(this, aParams);
+      break;
+
+    case FileRequestParams::TFileRequestTruncateParams:
+      actor = new TruncateOp(this, aParams);
+      break;
+
+    case FileRequestParams::TFileRequestFlushParams:
+      actor = new FlushOp(this, aParams);
+      break;
+
+    case FileRequestParams::TFileRequestGetFileParams:
+      actor = new GetFileOp(this, aParams);
+      break;
+
+    default:
+      MOZ_CRASH("Should never get here!");
+  }
+
+  MOZ_ASSERT(actor);
+
+  // Transfer ownership to IPDL.
+  return actor.forget().take();
+}
+
+bool
+FileHandle::RecvPBackgroundFileRequestConstructor(
+                                           PBackgroundFileRequestParent* aActor,
+                                           const FileRequestParams& aParams)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(aParams.type() != FileRequestParams::T__None);
+
+  auto* op = static_cast<NormalFileHandleOp*>(aActor);
+
+  if (NS_WARN_IF(!op->Init(this))) {
+    op->Cleanup();
+    return false;
+  }
+
+  op->Enqueue();
+  return true;
+}
+
+bool
+FileHandle::DeallocPBackgroundFileRequestParent(
+                                           PBackgroundFileRequestParent* aActor)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  // Transfer ownership back from IPDL.
+  nsRefPtr<NormalFileHandleOp> actor =
+    dont_AddRef(static_cast<NormalFileHandleOp*>(aActor));
+  return true;
+}
+
+/*******************************************************************************
+ * Local class implementations
+ ******************************************************************************/
+
+void
+FileHandleOp::Enqueue()
+{
+  AssertIsOnOwningThread();
+
+  FileHandleThreadPool* fileHandleThreadPool =
+    GetFileHandleThreadPoolFor(mFileHandle->Storage());
+  MOZ_ASSERT(fileHandleThreadPool);
+
+  fileHandleThreadPool->Enqueue(mFileHandle, this, false);
+
+  mFileHandle->NoteActiveRequest();
+}
+
+void
+FileHandle::
+FinishOp::RunOnThreadPool()
+{
+  AssertIsOnThreadPool();
+  MOZ_ASSERT(mFileHandle);
+
+  nsCOMPtr<nsISupports>& stream = mFileHandle->mStream;
+
+  if (!stream) {
+    return;
+  }
+
+  nsCOMPtr<nsIInputStream> inputStream = do_QueryInterface(stream);
+  MOZ_ASSERT(inputStream);
+
+  MOZ_ALWAYS_TRUE(NS_SUCCEEDED(inputStream->Close()));
+
+  stream = nullptr;
+}
+
+void
+FileHandle::
+FinishOp::RunOnOwningThread()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileHandle);
+
+  mFileHandle->SendCompleteNotification(mAborted);
+
+  mFileHandle->GetMutableFile()->UnregisterFileHandle(mFileHandle);
+
+  mFileHandle = nullptr;
+}
+
+NormalFileHandleOp::~NormalFileHandleOp()
+{
+  MOZ_ASSERT(!mFileHandle,
+             "NormalFileHandleOp::Cleanup() was not called by a subclass!");
+}
+
+bool
+NormalFileHandleOp::Init(FileHandle* aFileHandle)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+
+  nsresult rv = aFileHandle->GetOrCreateStream(getter_AddRefs(mFileStream));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return false;
+  }
+
+  return true;
+}
+
+void
+NormalFileHandleOp::Cleanup()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileHandle);
+  MOZ_ASSERT_IF(!IsActorDestroyed(), mResponseSent);
+
+  mFileHandle = nullptr;
+}
+
+nsresult
+NormalFileHandleOp::SendSuccessResult()
+{
+  AssertIsOnOwningThread();
+
+  if (!IsActorDestroyed()) {
+    FileRequestResponse response;
+    GetResponse(response);
+
+    MOZ_ASSERT(response.type() != FileRequestResponse::T__None);
+
+    if (response.type() == FileRequestResponse::Tnsresult) {
+      MOZ_ASSERT(NS_FAILED(response.get_nsresult()));
+
+      return response.get_nsresult();
+    }
+
+    if (NS_WARN_IF(!PBackgroundFileRequestParent::Send__delete__(this,
+                                                                 response))) {
+      return NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+  }
+
+  DEBUGONLY(mResponseSent = true;)
+
+  return NS_OK;
+}
+
+bool
+NormalFileHandleOp::SendFailureResult(nsresult aResultCode)
+{
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(NS_FAILED(aResultCode));
+
+  bool result = false;
+
+  if (!IsActorDestroyed()) {
+    result =
+      PBackgroundFileRequestParent::Send__delete__(this, aResultCode);
+  }
+
+  DEBUGONLY(mResponseSent = true;)
+
+  return result;
+}
+
+void
+NormalFileHandleOp::RunOnThreadPool()
+{
+  AssertIsOnThreadPool();
+  MOZ_ASSERT(mFileHandle);
+  MOZ_ASSERT(NS_SUCCEEDED(mResultCode));
+
+  // There are several cases where we don't actually have to to any work here.
+
+  if (mFileHandleIsAborted) {
+    // This transaction is already set to be aborted.
+    mResultCode = NS_ERROR_DOM_FILEHANDLE_ABORT_ERR;
+  } else if (mFileHandle->IsInvalidatedOnAnyThread()) {
+    // This file handle is being invalidated.
+    mResultCode = NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+  } else if (!OperationMayProceed()) {
+    // The operation was canceled in some way, likely because the child process
+    // has crashed.
+    mResultCode = NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+  } else {
+    nsresult rv = DoFileWork(mFileHandle);
+    if (NS_FAILED(rv)) {
+      mResultCode = rv;
+    }
+  }
+}
+
+void
+NormalFileHandleOp::RunOnOwningThread()
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(mFileHandle);
+
+  if (NS_WARN_IF(IsActorDestroyed())) {
+    // Don't send any notifications if the actor was destroyed already.
+    if (NS_SUCCEEDED(mResultCode)) {
+      mResultCode = NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    }
+  } else {
+    if (mFileHandle->IsInvalidated()) {
+      mResultCode = NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    } else if (mFileHandle->IsAborted()) {
+      // Aborted file handles always see their requests fail with ABORT_ERR,
+      // even if the request succeeded or failed with another error.
+      mResultCode = NS_ERROR_DOM_FILEHANDLE_ABORT_ERR;
+    } else if (NS_SUCCEEDED(mResultCode)) {
+      // This may release the IPDL reference.
+      mResultCode = SendSuccessResult();
+    }
+
+    if (NS_FAILED(mResultCode)) {
+      // This should definitely release the IPDL reference.
+      if (!SendFailureResult(mResultCode)) {
+        // Abort the file handle.
+        mFileHandle->Abort(/* aForce */ false);
+      }
+    }
+  }
+
+  mFileHandle->NoteFinishedRequest();
+
+  Cleanup();
+}
+
+void
+NormalFileHandleOp::ActorDestroy(ActorDestroyReason aWhy)
+{
+  AssertIsOnOwningThread();
+
+  NoteActorDestroyed();
+}
+
+nsresult
+CopyFileHandleOp::DoFileWork(FileHandle* aFileHandle)
+{
+  AssertIsOnThreadPool();
+
+  nsCOMPtr<nsIInputStream> inputStream;
+  nsCOMPtr<nsIOutputStream> outputStream;
+
+  if (mRead) {
+    inputStream = do_QueryInterface(mFileStream);
+    outputStream = do_QueryInterface(mBufferStream);
+  } else {
+    inputStream = do_QueryInterface(mBufferStream);
+    outputStream = do_QueryInterface(mFileStream);
+  }
+
+  MOZ_ASSERT(inputStream);
+  MOZ_ASSERT(outputStream);
+
+  nsCOMPtr<nsISeekableStream> seekableStream =
+    do_QueryInterface(mFileStream);
+
+  nsresult rv;
+
+  if (seekableStream) {
+    if (mOffset == UINT64_MAX) {
+      rv = seekableStream->Seek(nsISeekableStream::NS_SEEK_END, 0);
+    }
+    else {
+      rv = seekableStream->Seek(nsISeekableStream::NS_SEEK_SET, mOffset);
+    }
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  mOffset = 0;
+
+  do {
+    char copyBuffer[kStreamCopyBlockSize];
+
+    uint64_t max = mSize - mOffset;
+    if (max == 0) {
+      break;
+    }
+
+    uint32_t count = sizeof(copyBuffer);
+    if (count > max) {
+      count = max;
+    }
+
+    uint32_t numRead;
+    rv = inputStream->Read(copyBuffer, count, &numRead);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    if (!numRead) {
+      break;
+    }
+
+    uint32_t numWrite;
+    rv = outputStream->Write(copyBuffer, numRead, &numWrite);
+    if (rv == NS_ERROR_FILE_NO_DEVICE_SPACE) {
+      rv = NS_ERROR_DOM_FILEHANDLE_QUOTA_ERR;
+    }
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    if (NS_WARN_IF(numWrite != numRead)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    mOffset += numWrite;
+
+    nsCOMPtr<nsIRunnable> runnable =
+      new ProgressRunnable(this, mOffset, mSize);
+
+    mOwningThread->Dispatch(runnable, NS_DISPATCH_NORMAL);
+  } while (true);
+
+  MOZ_ASSERT(mOffset == mSize);
+
+  if (mRead) {
+    MOZ_ALWAYS_TRUE(NS_SUCCEEDED(outputStream->Close()));
+  } else {
+    MOZ_ALWAYS_TRUE(NS_SUCCEEDED(inputStream->Close()));
+  }
+
+  return NS_OK;
+}
+
+void
+CopyFileHandleOp::Cleanup()
+{
+  AssertIsOnOwningThread();
+
+  mBufferStream = nullptr;
+
+  NormalFileHandleOp::Cleanup();
+}
+
+NS_IMETHODIMP
+CopyFileHandleOp::
+ProgressRunnable::Run()
+{
+  AssertIsOnBackgroundThread();
+
+  unused << mCopyFileHandleOp->SendProgress(mProgress, mProgressMax);
+
+  mCopyFileHandleOp = nullptr;
+
+  return NS_OK;
+}
+
+GetMetadataOp::GetMetadataOp(FileHandle* aFileHandle,
+                             const FileRequestParams& aParams)
+  : NormalFileHandleOp(aFileHandle)
+  , mParams(aParams.get_FileRequestGetMetadataParams())
+{
+  MOZ_ASSERT(aParams.type() ==
+             FileRequestParams::TFileRequestGetMetadataParams);
+}
+
+nsresult
+GetMetadataOp::DoFileWork(FileHandle* aFileHandle)
+{
+  AssertIsOnThreadPool();
+
+  nsresult rv;
+
+  if (mFileHandle->Mode() == FileMode::Readwrite) {
+    // Force a flush (so all pending writes are flushed to the disk and file
+    // metadata is updated too).
+
+    nsCOMPtr<nsIOutputStream> ostream = do_QueryInterface(mFileStream);
+    MOZ_ASSERT(ostream);
+
+    rv = ostream->Flush();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  nsCOMPtr<nsIFileMetadata> metadata = do_QueryInterface(mFileStream);
+  MOZ_ASSERT(metadata);
+
+  if (mParams.size()) {
+    int64_t size;
+    rv = metadata->GetSize(&size);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    if (NS_WARN_IF(size < 0)) {
+      return NS_ERROR_FAILURE;
+    }
+
+    mMetadata.size() = uint64_t(size);
+  } else {
+    mMetadata.size() = void_t();
+  }
+
+  if (mParams.lastModified()) {
+    int64_t lastModified;
+    rv = metadata->GetLastModified(&lastModified);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    mMetadata.lastModified() = lastModified;
+  } else {
+    mMetadata.lastModified() = void_t();
+  }
+
+  return NS_OK;
+}
+
+void
+GetMetadataOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  aResponse = FileRequestGetMetadataResponse(mMetadata);
+}
+
+ReadOp::ReadOp(FileHandle* aFileHandle,
+               const FileRequestParams& aParams)
+  : CopyFileHandleOp(aFileHandle)
+  , mParams(aParams.get_FileRequestReadParams())
+{
+  MOZ_ASSERT(aParams.type() == FileRequestParams::TFileRequestReadParams);
+}
+
+bool
+ReadOp::Init(FileHandle* aFileHandle)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+
+  if (NS_WARN_IF(!NormalFileHandleOp::Init(aFileHandle))) {
+    return false;
+  }
+
+  mBufferStream = MemoryOutputStream::Create(mParams.size());
+  if (NS_WARN_IF(!mBufferStream)) {
+    return false;
+  }
+
+  mOffset = mParams.offset();
+  mSize = mParams.size();
+  mRead = true;
+
+  return true;
+}
+
+void
+ReadOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  auto* stream = static_cast<MemoryOutputStream*>(mBufferStream.get());
+
+  aResponse = FileRequestReadResponse(stream->Data());
+}
+
+// static
+already_AddRefed<ReadOp::MemoryOutputStream>
+ReadOp::
+MemoryOutputStream::Create(uint64_t aSize)
+{
+  MOZ_ASSERT(aSize, "Passed zero size!");
+
+  if (NS_WARN_IF(aSize > UINT32_MAX)) {
+    return nullptr;
+  }
+
+  nsRefPtr<MemoryOutputStream> stream = new MemoryOutputStream();
+
+  char* dummy;
+  uint32_t length = stream->mData.GetMutableData(&dummy, aSize, fallible);
+  if (NS_WARN_IF(length != aSize)) {
+    return nullptr;
+  }
+
+  return stream.forget();
+}
+
+NS_IMPL_ISUPPORTS(ReadOp::MemoryOutputStream, nsIOutputStream)
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::Close()
+{
+  mData.Truncate(mOffset);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::Write(const char* aBuf, uint32_t aCount, uint32_t* _retval)
+{
+  return WriteSegments(NS_CopySegmentToBuffer, (char*)aBuf, aCount, _retval);
+}
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::Flush()
+{
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::WriteFrom(nsIInputStream* aFromStream, uint32_t aCount,
+                              uint32_t* _retval)
+{
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::WriteSegments(nsReadSegmentFun aReader, void* aClosure,
+                                  uint32_t aCount, uint32_t* _retval)
+{
+  NS_ASSERTION(mData.Length() >= mOffset, "Bad stream state!");
+
+  uint32_t maxCount = mData.Length() - mOffset;
+  if (maxCount == 0) {
+    *_retval = 0;
+    return NS_OK;
+  }
+
+  if (aCount > maxCount) {
+    aCount = maxCount;
+  }
+
+  nsresult rv = aReader(this, aClosure, mData.BeginWriting() + mOffset, 0,
+                        aCount, _retval);
+  if (NS_SUCCEEDED(rv)) {
+    NS_ASSERTION(*_retval <= aCount,
+                 "Reader should not read more than we asked it to read!");
+    mOffset += *_retval;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ReadOp::
+MemoryOutputStream::IsNonBlocking(bool* _retval)
+{
+  *_retval = false;
+  return NS_OK;
+}
+
+WriteOp::WriteOp(FileHandle* aFileHandle,
+                 const FileRequestParams& aParams)
+  : CopyFileHandleOp(aFileHandle)
+  , mParams(aParams.get_FileRequestWriteParams())
+{
+  MOZ_ASSERT(aParams.type() == FileRequestParams::TFileRequestWriteParams);
+}
+
+bool
+WriteOp::Init(FileHandle* aFileHandle)
+{
+  AssertIsOnOwningThread();
+  MOZ_ASSERT(aFileHandle);
+
+  if (NS_WARN_IF(!NormalFileHandleOp::Init(aFileHandle))) {
+    return false;
+  }
+
+  nsCOMPtr<nsIInputStream> inputStream;
+
+  const FileRequestData& data = mParams.data();
+  switch (data.type()) {
+    case FileRequestData::TFileRequestStringData: {
+      const FileRequestStringData& stringData =
+        data.get_FileRequestStringData();
+
+      const nsCString& string = stringData.string();
+
+      nsresult rv =
+        NS_NewCStringInputStream(getter_AddRefs(inputStream), string);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return false;
+      }
+
+      break;
+    }
+    case FileRequestData::TFileRequestBlobData: {
+      const FileRequestBlobData& blobData =
+        data.get_FileRequestBlobData();
+
+      auto blobActor = static_cast<BlobParent*>(blobData.blobParent());
+
+      nsRefPtr<BlobImpl> blobImpl = blobActor->GetBlobImpl();
+
+      ErrorResult rv;
+      blobImpl->GetInternalStream(getter_AddRefs(inputStream), rv);
+      if (NS_WARN_IF(rv.Failed())) {
+        return false;
+      }
+
+      break;
+    }
+
+    default:
+      MOZ_CRASH("Should never get here!");
+  }
+
+  mBufferStream = inputStream;
+  mOffset = mParams.offset();
+  mSize = mParams.dataLength();
+  mRead = false;
+
+  return true;
+}
+
+void
+WriteOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+  aResponse = FileRequestWriteResponse();
+}
+
+TruncateOp::TruncateOp(FileHandle* aFileHandle,
+                       const FileRequestParams& aParams)
+  : NormalFileHandleOp(aFileHandle)
+  , mParams(aParams.get_FileRequestTruncateParams())
+{
+  MOZ_ASSERT(aParams.type() == FileRequestParams::TFileRequestTruncateParams);
+}
+
+nsresult
+TruncateOp::DoFileWork(FileHandle* aFileHandle)
+{
+  AssertIsOnThreadPool();
+
+  nsCOMPtr<nsISeekableStream> sstream = do_QueryInterface(mFileStream);
+  MOZ_ASSERT(sstream);
+
+  nsresult rv = sstream->Seek(nsISeekableStream::NS_SEEK_SET, mParams.offset());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  rv = sstream->SetEOF();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+void
+TruncateOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+  aResponse = FileRequestTruncateResponse();
+}
+
+FlushOp::FlushOp(FileHandle* aFileHandle,
+                 const FileRequestParams& aParams)
+  : NormalFileHandleOp(aFileHandle)
+  , mParams(aParams.get_FileRequestFlushParams())
+{
+  MOZ_ASSERT(aParams.type() == FileRequestParams::TFileRequestFlushParams);
+}
+
+nsresult
+FlushOp::DoFileWork(FileHandle* aFileHandle)
+{
+  AssertIsOnThreadPool();
+
+  nsCOMPtr<nsIOutputStream> ostream = do_QueryInterface(mFileStream);
+  MOZ_ASSERT(ostream);
+
+  nsresult rv = ostream->Flush();
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+void
+FlushOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+  aResponse = FileRequestFlushResponse();
+}
+
+GetFileOp::GetFileOp(FileHandle* aFileHandle,
+                     const FileRequestParams& aParams)
+  : GetMetadataOp(aFileHandle,
+                  FileRequestGetMetadataParams(true, true))
+  , mBackgroundParent(aFileHandle->GetBackgroundParent())
+{
+  MOZ_ASSERT(aParams.type() == FileRequestParams::TFileRequestGetFileParams);
+  MOZ_ASSERT(mBackgroundParent);
+}
+
+void
+GetFileOp::GetResponse(FileRequestResponse& aResponse)
+{
+  AssertIsOnOwningThread();
+
+  nsRefPtr<BlobImpl> blobImpl = mFileHandle->GetMutableFile()->CreateBlobImpl();
+  MOZ_ASSERT(blobImpl);
+
+  PBlobParent* actor =
+    BackgroundParent::GetOrCreateActorForBlobImpl(mBackgroundParent, blobImpl);
+  if (NS_WARN_IF(!actor)) {
+    // This can only fail if the child has crashed.
+    aResponse = NS_ERROR_DOM_FILEHANDLE_UNKNOWN_ERR;
+    return;
+  }
+
+  FileRequestGetFileResponse response;
+  response.fileParent() = actor;
+  response.metadata() = mMetadata;
+
+  aResponse = response;
+}
+
+} // namespace dom
+} // namespace mozilla