author Ryan Hunt <>
Mon, 05 Jun 2017 19:45:31 -0500
changeset 366287 70136b7cb54b75cd105f7d6e6a92d9dd0240162f
parent 366285 8d3d222b4761f2c6cfe27c92ba0ae1dcf3c44430
child 366846 8ec5e890bcbd5b688b53c85067846411ff48311b
permissions -rw-r--r--
Bug 1351783 part 12 - Create and sync focus sequence numbers. r=kats,botond,dvander Focus can change at any moment in a document. This causes non-determinism and correctness problems for doing keyboard apz scrolling. To get around this, we will maintain deterministic behavior for focus changes initiated by input events and see if we can get away with more non-determinism for things like `setTimeout` In order to do this, we disable async keyboard scrolling when an input event is processed that could have a event listener. We then attach a sequence number to that input event and dispatch it to content. In content, we record the highest sequence number that we have processed from an event, and send that on each focus update. Using this, we can determine in APZ if we have a current focus target or if we are still waiting for an input event to be processed and focus to be reconfirmed. MozReview-Commit-ID: CWcu8YEFQz4

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * 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
 * This Original Code has been modified by IBM Corporation.
 * Modifications made by IBM described herein are
 * Copyright (c) International Business Machines
 * Corporation, 2000
 * Modifications to Mozilla code or documentation
 * identified per MPL Section 3.3
 * Date         Modified by     Description of modification
 * 05/03/2000   IBM Corp.       Observer related defines for reflow

/* a presentation of a document, part 2 */

#ifndef nsIPresShell_h___
#define nsIPresShell_h___

#include "mozilla/ArenaObjectID.h"
#include "mozilla/EventForwards.h"
#include "mozilla/FlushType.h"
#include "mozilla/layers/FocusTarget.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/StaticPtr.h"
#include "mozilla/StyleSetHandle.h"
#include "mozilla/StyleSheet.h"
#include "mozilla/WeakPtr.h"
#include "gfxPoint.h"
#include "nsTHashtable.h"
#include "nsHashKeys.h"
#include "nsISupports.h"
#include "nsIContent.h"
#include "nsISelectionController.h"
#include "nsQueryFrame.h"
#include "nsCoord.h"
#include "nsColor.h"
#include "nsFrameManagerBase.h"
#include "nsRect.h"
#include "nsRegionFwd.h"
#include "nsWeakReference.h"
#include <stdio.h> // for FILE definition
#include "nsChangeHint.h"
#include "nsRefPtrHashtable.h"
#include "nsClassHashtable.h"
#include "nsPresArena.h"
#include "nsIImageLoadingContent.h"
#include "nsMargin.h"
#include "nsFrameState.h"
#include "Units.h"

class gfxContext;
class nsDocShell;
class nsIDocument;
class nsIFrame;
class nsPresContext;
class nsViewManager;
class nsView;
class nsIPageSequenceFrame;
class nsCanvasFrame;
class nsAString;
class nsCaret;
namespace mozilla {
class AccessibleCaretEventHub;
class CSSStyleSheet;
} // namespace mozilla
class nsFrameSelection;
class nsFrameManager;
class nsILayoutHistoryState;
class nsIReflowCallback;
class nsIDOMNode;
class nsCSSFrameConstructor;
class nsISelection;
template<class E> class nsCOMArray;
class AutoWeakFrame;
class WeakFrame;
class nsIScrollableFrame;
class nsIDOMEvent;
class nsDisplayList;
class nsDisplayListBuilder;
class nsPIDOMWindowOuter;
struct nsPoint;
class nsINode;
struct nsRect;
class nsRegion;
class nsRefreshDriver;
class nsARefreshObserver;
class nsAPostRefreshObserver;
class nsAccessibilityService;
namespace mozilla {
namespace a11y {
class DocAccessible;
} // namespace a11y
} // namespace mozilla
struct nsArenaMemoryStats;
class nsITimer;

namespace mozilla {
class EventStates;

namespace dom {
class Element;
class Touch;
class Selection;
class ShadowRoot;
} // namespace dom

namespace layers {
class LayerManager;
} // namespace layers

namespace gfx {
class SourceSurface;
} // namespace gfx
} // namespace mozilla

// Flags to pass to SetCapturingContent
// when assigning capture, ignore whether capture is allowed or not
// true if events should be targeted at the capturing content or its children
// true if the current capture wants drags to be prevented
// true when the mouse is pointer locked, and events are sent to locked element

typedef struct CapturingContentInfo {
  // capture should only be allowed during a mousedown event
  bool mAllowed;
  bool mPointerLock;
  bool mRetargetToElement;
  bool mPreventDrag;
  mozilla::StaticRefPtr<nsIContent> mContent;
} CapturingContentInfo;

// a75573d6-34c8-4485-8fb7-edcb6fc70e12
{ 0xa75573d6, 0x34c8, 0x4485, \
  { 0x8f, 0xb7, 0xed, 0xcb, 0x6f, 0xc7, 0x0e, 0x12 } }

// debug VerifyReflow flags
#define VERIFY_REFLOW_ON                    0x01
#define VERIFY_REFLOW_NOISY                 0x02
#define VERIFY_REFLOW_ALL                   0x04
#define VERIFY_REFLOW_DUMP_COMMANDS         0x08
#define VERIFY_REFLOW_NOISY_RC              0x10


enum nsRectVisibility {

 * Presentation shell interface. Presentation shells are the
 * controlling point for managing the presentation of a document. The
 * presentation shell holds a live reference to the document, the
 * presentation context, the style manager, the style set and the root
 * frame. <p>
 * When this object is Release'd, it will release the document, the
 * presentation context, the style manager, the style set and the root
 * frame.

class nsIPresShell : public nsISupports

  typedef mozilla::layers::FocusTarget FocusTarget;
  typedef mozilla::layers::LayerManager LayerManager;
  typedef mozilla::gfx::SourceSurface SourceSurface;

  enum eRenderFlag {
  typedef uint8_t RenderFlags; // for storing the above flags


   * All callers are responsible for calling |Destroy| after calling
   * |EndObservingDocument|.  It needs to be separate only because form
   * controls incorrectly store their data in the frames rather than the
   * content model and printing calls |EndObservingDocument| multiple
   * times to make form controls behave nicely when printed.
  virtual void Destroy() = 0;

  bool IsDestroying() { return mIsDestroying; }

   * All frames owned by the shell are allocated from an arena.  They
   * are also recycled using free lists.  Separate free lists are
   * maintained for each frame type (aID), which must always correspond
   * to the same aSize value.  AllocateFrame is infallible and will abort
   * on out-of-memory.
  void* AllocateFrame(nsQueryFrame::FrameIID aID, size_t aSize)
    void* result = mFrameArena.AllocateByFrameID(aID, aSize);
    return result;

  void FreeFrame(nsQueryFrame::FrameIID aID, void* aPtr)
    if (!mIsDestroying)
      mFrameArena.FreeByFrameID(aID, aPtr);

   * This is for allocating other types of objects (not frames).  Separate free
   * lists are maintained for each type (aID), which must always correspond to
   * the same aSize value.  AllocateByObjectID is infallible and will abort on
   * out-of-memory.
  void* AllocateByObjectID(mozilla::ArenaObjectID aID, size_t aSize)
    void* result = mFrameArena.AllocateByObjectID(aID, aSize);
    return result;

  void FreeByObjectID(mozilla::ArenaObjectID aID, void* aPtr)
    if (!mIsDestroying)
      mFrameArena.FreeByObjectID(aID, aPtr);

  template<typename T>
  void RegisterArenaRefPtr(mozilla::ArenaRefPtr<T>* aPtr)

  template<typename T>
  void DeregisterArenaRefPtr(mozilla::ArenaRefPtr<T>* aPtr)

  void ClearArenaRefPtrs(mozilla::ArenaObjectID aObjectID)

  nsIDocument* GetDocument() const { return mDocument; }

  nsPresContext* GetPresContext() const { return mPresContext; }

  nsViewManager* GetViewManager() const { return mViewManager; }

  nsRefreshDriver* GetRefreshDriver() const;

   * Return the document accessible for this pres shell if there is one.
  mozilla::a11y::DocAccessible* GetDocAccessible() const
    return mDocAccessible;

   * Set the document accessible for this pres shell.
  void SetDocAccessible(mozilla::a11y::DocAccessible* aDocAccessible)
    mDocAccessible = aDocAccessible;

  mozilla::StyleSetHandle StyleSet() const { return mStyleSet; }

  nsCSSFrameConstructor* FrameConstructor() const { return mFrameConstructor; }

  nsFrameManager* FrameManager() const {
    // reinterpret_cast is valid since nsFrameManager does not add
    // any members over nsFrameManagerBase.
    return reinterpret_cast<nsFrameManager*>


  /* Enable/disable author style level. Disabling author style disables the entire
   * author level of the cascade, including the HTML preshint level.
  // XXX these could easily be inlined, but there is a circular #include
  // problem with nsStyleSet.
  void SetAuthorStyleDisabled(bool aDisabled);
  bool GetAuthorStyleDisabled() const;

   * Called when stylesheets are added/removed/enabled/disabled to
   * recompute style and clear other cached data as needed.  This will
   * not reconstruct style synchronously; if you need to do that, call
   * FlushPendingNotifications to flush out style reresolves.
   * This handles the the addition and removal of the various types of
   * style rules that can be in CSS style sheets, such as @font-face
   * rules and @counter-style rules.
   * It requires that StyleSheetAdded, StyleSheetRemoved,
   * StyleSheetApplicableStateChanged, StyleRuleAdded, StyleRuleRemoved,
   * or StyleRuleChanged has been called on the style sheets that have
   * changed.
   * // XXXbz why do we have this on the interface anyway?  The only consumer
   * is calling AddOverrideStyleSheet/RemoveOverrideStyleSheet, and I think
   * those should just handle reconstructing style data...
  void RestyleForCSSRuleChanges();

   * Update the style set somehow to take into account changed prefs which
   * affect document styling.
  virtual void UpdatePreferenceStyles() = 0;

   * FrameSelection will return the Frame based selection API.
   * You cannot go back and forth anymore with QI between nsIDOM sel and
   * nsIFrame sel.
  already_AddRefed<nsFrameSelection> FrameSelection();

   * ConstFrameSelection returns an object which methods are safe to use for
   * example in nsIFrame code.
  const nsFrameSelection* ConstFrameSelection() const { return mSelection; }

  // Make shell be a document observer.  If called after Destroy() has
  // been called on the shell, this will be ignored.
  virtual void BeginObservingDocument() = 0;

  // Make shell stop being a document observer
  virtual void EndObservingDocument() = 0;

   * Return whether Initialize() was previously called.
  bool DidInitialize() const { return mDidInitialize; }

   * Perform initialization. Constructs the frame for the root content
   * object and then enqueues a reflow of the frame model into the
   * specified width and height.
   * The coordinates for aWidth and aHeight must be in standard nscoords.
   * Callers of this method must hold a reference to this shell that
   * is guaranteed to survive through arbitrary script execution.
   * Calling Initialize can execute arbitrary script.
  virtual nsresult Initialize(nscoord aWidth, nscoord aHeight) = 0;

   * Reflow the frame model into a new width and height.  The
   * coordinates for aWidth and aHeight must be in standard nscoord's.
  virtual nsresult ResizeReflow(nscoord aWidth, nscoord aHeight, nscoord aOldWidth = 0, nscoord aOldHeight = 0) = 0;
   * Do the same thing as ResizeReflow but even if ResizeReflowOverride was
   * called previously.
  virtual nsresult ResizeReflowIgnoreOverride(nscoord aWidth, nscoord aHeight, nscoord aOldWidth, nscoord aOldHeight) = 0;

   * Returns true if ResizeReflowOverride has been called.
  virtual bool GetIsViewportOverridden() = 0;

   * Return true if the presshell expects layout flush.
  virtual bool IsLayoutFlushObserver() = 0;

   * Called when document load completes.
  virtual void LoadComplete() = 0;

   * This calls through to the frame manager to get the root frame.
  virtual nsIFrame* GetRootFrameExternal() const;
  nsIFrame* GetRootFrame() const {
    return mFrameManager->GetRootFrame();
    return GetRootFrameExternal();

   * Get root scroll frame from FrameManager()->GetRootFrame().
  nsIFrame* GetRootScrollFrame() const;

   * The same as GetRootScrollFrame, but returns an nsIScrollableFrame
  nsIScrollableFrame* GetRootScrollFrameAsScrollable() const;

   * The same as GetRootScrollFrame, but returns an nsIScrollableFrame.
   * Can be called by code not linked into gklayout.
  virtual nsIScrollableFrame* GetRootScrollFrameAsScrollableExternal() const;

   * Get the current focused content or DOM selection that should be the
   * target for scrolling.
  already_AddRefed<nsIContent> GetContentForScrolling() const;

   * Gets nearest scrollable frame from the specified content node. The frame
   * is scrollable with overflow:scroll or overflow:auto in some direction when
   * aDirection is eEither.  Otherwise, this returns a nearest frame that is
   * scrollable in the specified direction.
  enum ScrollDirection { eHorizontal, eVertical, eEither };
  nsIScrollableFrame* GetScrollableFrameToScrollForContent(
                         nsIContent* aContent,
                         ScrollDirection aDirection);

   * Gets nearest scrollable frame from current focused content or DOM
   * selection if there is no focused content. The frame is scrollable with
   * overflow:scroll or overflow:auto in some direction when aDirection is
   * eEither.  Otherwise, this returns a nearest frame that is scrollable in
   * the specified direction.
  nsIScrollableFrame* GetScrollableFrameToScroll(ScrollDirection aDirection);

   * Returns the page sequence frame associated with the frame hierarchy.
   * Returns nullptr if not a paginated view.
  virtual nsIPageSequenceFrame* GetPageSequenceFrame() const = 0;

  * Returns the canvas frame associated with the frame hierarchy.
  * Returns nullptr if is XUL document.
  virtual nsCanvasFrame* GetCanvasFrame() const = 0;

   * Tell the pres shell that a frame needs to be marked dirty and needs
   * Reflow.  It's OK if this is an ancestor of the frame needing reflow as
   * long as the ancestor chain between them doesn't cross a reflow root.
   * The bit to add should be NS_FRAME_IS_DIRTY, NS_FRAME_HAS_DIRTY_CHILDREN
   * or nsFrameState(0); passing 0 means that dirty bits won't be set on the
   * frame or its ancestors/descendants, but that intrinsic widths will still
   * be marked dirty.  Passing aIntrinsicDirty = eResize and aBitToAdd = 0
   * would result in no work being done, so don't do that.
  enum IntrinsicDirty {
    // XXXldb eResize should be renamed
    eResize,     // don't mark any intrinsic widths dirty
    eTreeChange, // mark intrinsic widths dirty on aFrame and its ancestors
    eStyleChange // Do eTreeChange, plus all of aFrame's descendants
  enum ReflowRootHandling {
    ePositionOrSizeChange, // aFrame is changing position or size
    eNoPositionOrSizeChange, // ... NOT changing ...
    eInferFromBitToAdd // is changing iff (aBitToAdd == NS_FRAME_IS_DIRTY)

    // Note:  With eStyleChange, these can also apply to out-of-flows
    // in addition to aFrame.
  virtual void FrameNeedsReflow(nsIFrame *aFrame,
                                IntrinsicDirty aIntrinsicDirty,
                                nsFrameState aBitToAdd,
                                ReflowRootHandling aRootHandling =
                                  eInferFromBitToAdd) = 0;

   * Calls FrameNeedsReflow on all fixed position children of the root frame.
  virtual void MarkFixedFramesForReflow(IntrinsicDirty aIntrinsicDirty);

   * Tell the presshell that the given frame's reflow was interrupted.  This
   * will mark as having dirty children a path from the given frame (inclusive)
   * to the nearest ancestor with a dirty subtree, or to the reflow root
   * currently being reflowed if no such ancestor exists (inclusive).  This is
   * to be done immediately after reflow of the current reflow root completes.
   * This method must only be called during reflow, and the frame it's being
   * called on must be in the process of being reflowed when it's called.  This
   * method doesn't mark any intrinsic widths dirty and doesn't add any bits
  virtual void FrameNeedsToContinueReflow(nsIFrame *aFrame) = 0;

  virtual void CancelAllPendingReflows() = 0;

  virtual void NotifyCounterStylesAreDirty() = 0;

   * Destroy the frames for aContent.  Note that this may destroy frames
   * for an ancestor instead - aDestroyedFramesFor contains the content node
   * where frames were actually destroyed (which should be used in the
   * CreateFramesFor call).  The frame tree state will be captured before
   * the frames are destroyed in the frame constructor.
  virtual void DestroyFramesFor(nsIContent*  aContent,
                                nsIContent** aDestroyedFramesFor) = 0;
   * Create new frames for aContent.  It will use the last captured layout
   * history state captured in the frame constructor to restore the state
   * in the new frame tree.
  virtual void CreateFramesFor(nsIContent* aContent) = 0;

  void PostRecreateFramesFor(mozilla::dom::Element* aElement);
  void RestyleForAnimation(mozilla::dom::Element* aElement,
                           nsRestyleHint aHint);

  // ShadowRoot has APIs that can change styles so we only
  // want to restyle elements in the ShadowRoot and not the whole
  // document.
  virtual void RecordShadowStyleChange(mozilla::dom::ShadowRoot* aShadowRoot) = 0;

   * Determine if it is safe to flush all pending notifications
   * @param aIsSafeToFlush true if it is safe, false otherwise.
  virtual bool IsSafeToFlush() const = 0;

   * Flush pending notifications of the type specified.  This method
   * will not affect the content model; it'll just affect style and
   * frames. Callers that actually want up-to-date presentation (other
   * than the document itself) should probably be calling
   * nsIDocument::FlushPendingNotifications.
   * This method can execute script, which can destroy this presshell object
   * unless someone is holding a reference to it on the stack.  The presshell
   * itself will ensure it lives up until the method returns, but callers who
   * plan to use the presshell after this call should hold a strong ref
   * themselves!
   * @param aType the type of notifications to flush
  void FlushPendingNotifications(mozilla::FlushType aType)
    if (!NeedFlush(aType)) {


  void FlushPendingNotifications(mozilla::ChangesToFlush aType)
    if (!NeedFlush(aType.mFlushType)) {


   * Implementation methods for FlushPendingNotifications.
  virtual void DoFlushPendingNotifications(mozilla::FlushType aType) = 0;
  virtual void DoFlushPendingNotifications(mozilla::ChangesToFlush aType) = 0;

   * Whether we might need a flush for the given flush type.  If this
   * function returns false, we definitely don't need to flush.
   * @param aFlushType The flush type to check.  This must be
   *   >= FlushType::Style.  This also returns true if a throttled
   *   animation flush is required.
  bool NeedFlush(mozilla::FlushType aType) const
    // We check mInFlush to handle re-entrant calls to FlushPendingNotifications
    // by reporting that we always need a flush in that case.  Otherwise,
    // we could end up missing needed flushes, since we clear the mNeedXXXFlush
    // flags at the top of FlushPendingNotifications.
    MOZ_ASSERT(aType >= mozilla::FlushType::Style);
    return mNeedStyleFlush ||
           (mNeedLayoutFlush &&
            aType >= mozilla::FlushType::InterruptibleLayout) ||
           aType >= mozilla::FlushType::Display ||
           mNeedThrottledAnimationFlush ||

  inline void EnsureStyleFlush();
  inline void SetNeedStyleFlush();
  inline void SetNeedLayoutFlush();
  inline void SetNeedThrottledAnimationFlush();

  bool ObservingStyleFlushes() const { return mObservingStyleFlushes; }
  bool ObservingLayoutFlushes() const { return mObservingLayoutFlushes; }

  void ObserveStyleFlushes()
    if (!ObservingStyleFlushes())

  bool NeedStyleFlush() const { return mNeedStyleFlush; }

   * Callbacks will be called even if reflow itself fails for
   * some reason.
  virtual nsresult PostReflowCallback(nsIReflowCallback* aCallback) = 0;
  virtual void CancelReflowCallback(nsIReflowCallback* aCallback) = 0;

  virtual void ClearFrameRefs(nsIFrame* aFrame) = 0;

   * Get a reference rendering context. This is a context that should not
   * be rendered to, but is suitable for measuring text and performing
   * other non-rendering operations. Guaranteed to return non-null.
  virtual already_AddRefed<gfxContext> CreateReferenceRenderingContext() = 0;

   * Informs the pres shell that the document is now at the anchor with
   * the given name.  If |aScroll| is true, scrolls the view of the
   * document so that the anchor with the specified name is displayed at
   * the top of the window.  If |aAnchorName| is empty, then this informs
   * the pres shell that there is no current target, and |aScroll| must
   * be false.  If |aAdditionalScrollFlags| is nsIPresShell::SCROLL_SMOOTH_AUTO
   * and |aScroll| is true, the scrolling may be performed with an animation.
  virtual nsresult GoToAnchor(const nsAString& aAnchorName, bool aScroll,
                              uint32_t aAdditionalScrollFlags = 0) = 0;

   * Tells the presshell to scroll again to the last anchor scrolled to by
   * GoToAnchor, if any. This scroll only happens if the scroll
   * position has not changed since the last GoToAnchor. This is called
   * by nsDocumentViewer::LoadComplete. This clears the last anchor
   * scrolled to by GoToAnchor (we don't want to keep it alive if it's
   * removed from the DOM), so don't call this more than once.
  virtual nsresult ScrollToAnchor() = 0;

  enum {
    SCROLL_TOP     = 0,
    SCROLL_BOTTOM  = 100,
    SCROLL_LEFT    = 0,
    SCROLL_RIGHT   = 100,
    SCROLL_CENTER  = 50,

  enum WhenToScroll {
  typedef struct ScrollAxis {
    int16_t mWhereToScroll;
    WhenToScroll mWhenToScroll : 8;
    bool mOnlyIfPerceivedScrollableDirection : 1;
   * @param aWhere: Either a percentage or a special value.
   *                nsIPresShell defines:
   *                * (Default) SCROLL_MINIMUM = -1: The visible area is
   *                scrolled to show the entire frame. If the frame is too
   *                large, the top and left edges are given precedence.
   *                * SCROLL_TOP = 0: The frame's upper edge is aligned with the
   *                top edge of the visible area.
   *                * SCROLL_BOTTOM = 100: The frame's bottom edge is aligned
   *                with the bottom edge of the visible area.
   *                * SCROLL_LEFT = 0: The frame's left edge is aligned with the
   *                left edge of the visible area.
   *                * SCROLL_RIGHT = 100: The frame's right edge is aligned with
   *                the right edge of the visible area.
   *                * SCROLL_CENTER = 50: The frame is centered along the axis
   *                the ScrollAxis is used for.
   *                Other values are treated as a percentage, and the point
   *                "percent" down the frame is placed at the point "percent"
   *                down the visible area.
   * @param aWhen:
   *                * (Default) SCROLL_IF_NOT_FULLY_VISIBLE: Move the frame only
   *                if it is not fully visible (including if it's not visible
   *                at all). Note that in this case if the frame is too large to
   *                fit in view, it will only be scrolled if more of it can fit
   *                than is already in view.
   *                * SCROLL_IF_NOT_VISIBLE: Move the frame only if none of it
   *                is visible.
   *                * SCROLL_ALWAYS: Move the frame regardless of its current
   *                visibility.
   * @param aOnlyIfPerceivedScrollableDirection:
   *                If the direction is not a perceived scrollable direction (i.e.
   *                no scrollbar showing and less than one device pixel of
   *                scrollable distance), don't scroll. Defaults to false.
    explicit ScrollAxis(int16_t aWhere = SCROLL_MINIMUM,
                        WhenToScroll aWhen = SCROLL_IF_NOT_FULLY_VISIBLE,
                        bool aOnlyIfPerceivedScrollableDirection = false) :
      mWhereToScroll(aWhere), mWhenToScroll(aWhen),
  } ScrollAxis;
   * Scrolls the view of the document so that the primary frame of the content
   * is displayed in the window. Layout is flushed before scrolling.
   * @param aContent  The content object of which primary frame should be
   *                  scrolled into view.
   * @param aVertical How to align the frame vertically and when to do so.
   *                  This is a ScrollAxis of Where and When.
   * @param aHorizontal How to align the frame horizontally and when to do so.
   *                  This is a ScrollAxis of Where and When.
   * @param aFlags    If SCROLL_FIRST_ANCESTOR_ONLY is set, only the nearest
   *                  scrollable ancestor is scrolled, otherwise all
   *                  scrollable ancestors may be scrolled if necessary.
   *                  If SCROLL_OVERFLOW_HIDDEN is set then we may scroll in a
   *                  direction even if overflow:hidden is specified in that
   *                  direction; otherwise we will not scroll in that direction
   *                  when overflow:hidden is set for that direction.
   *                  If SCROLL_NO_PARENT_FRAMES is set then we only scroll
   *                  nodes in this document, not in any parent documents which
   *                  contain this document in a iframe or the like.
   *                  If SCROLL_SMOOTH is set and CSSOM-VIEW scroll-behavior
   *                  is enabled, we will scroll smoothly using
   *                  nsIScrollableFrame::ScrollMode::SMOOTH_MSD; otherwise,
   *                  nsIScrollableFrame::ScrollMode::INSTANT will be used.
   *                  If SCROLL_SMOOTH_AUTO is set, the CSSOM-View
   *                  scroll-behavior attribute is set to 'smooth' on the
   *                  scroll frame, and CSSOM-VIEW scroll-behavior is enabled,
   *                  we will scroll smoothly using
   *                  nsIScrollableFrame::ScrollMode::SMOOTH_MSD; otherwise,
   *                  nsIScrollableFrame::ScrollMode::INSTANT will be used.
  virtual nsresult ScrollContentIntoView(nsIContent* aContent,
                                                     ScrollAxis  aVertical,
                                                     ScrollAxis  aHorizontal,
                                                     uint32_t    aFlags) = 0;

  enum {
    SCROLL_SMOOTH = 0x08,
   * Scrolls the view of the document so that the given area of a frame
   * is visible, if possible. Layout is not flushed before scrolling.
   * @param aRect relative to aFrame
   * @param aVertical see ScrollContentIntoView and ScrollAxis
   * @param aHorizontal see ScrollContentIntoView and ScrollAxis
   * @param aFlags if SCROLL_FIRST_ANCESTOR_ONLY is set, only the
   * nearest scrollable ancestor is scrolled, otherwise all
   * scrollable ancestors may be scrolled if necessary
   * if SCROLL_OVERFLOW_HIDDEN is set then we may scroll in a direction
   * even if overflow:hidden is specified in that direction; otherwise
   * we will not scroll in that direction when overflow:hidden is
   * set for that direction
   * If SCROLL_NO_PARENT_FRAMES is set then we only scroll
   * nodes in this document, not in any parent documents which
   * contain this document in a iframe or the like.
   * @return true if any scrolling happened, false if no scrolling happened
  virtual bool ScrollFrameRectIntoView(nsIFrame*     aFrame,
                                       const nsRect& aRect,
                                       ScrollAxis    aVertical,
                                       ScrollAxis    aHorizontal,
                                       uint32_t      aFlags) = 0;

   * Determine if a rectangle specified in the frame's coordinate system
   * intersects the viewport "enough" to be considered visible.
   * @param aFrame frame that aRect coordinates are specified relative to
   * @param aRect rectangle in twips to test for visibility
   * @param aMinTwips is the minimum distance in from the edge of the viewport
   *                  that an object must be to be counted visible
   * @return nsRectVisibility_kVisible if the rect is visible
   *         nsRectVisibility_kAboveViewport
   *         nsRectVisibility_kBelowViewport
   *         nsRectVisibility_kLeftOfViewport
   *         nsRectVisibility_kRightOfViewport rectangle is outside the viewport
   *         in the specified direction
  virtual nsRectVisibility GetRectVisibility(nsIFrame *aFrame,
                                             const nsRect &aRect,
                                             nscoord aMinTwips) const = 0;

   * Suppress notification of the frame manager that frames are
   * being destroyed.
  virtual void SetIgnoreFrameDestruction(bool aIgnore) = 0;

   * Notification sent by a frame informing the pres shell that it is about to
   * be destroyed.
   * This allows any outstanding references to the frame to be cleaned up
  virtual void NotifyDestroyingFrame(nsIFrame* aFrame) = 0;

   * Get the AccessibleCaretEventHub, if it exists. AddRefs it.
  virtual already_AddRefed<mozilla::AccessibleCaretEventHub> GetAccessibleCaretEventHub() const = 0;

   * Get the caret, if it exists. AddRefs it.
  virtual already_AddRefed<nsCaret> GetCaret() const = 0;

   * Set the current caret to a new caret. To undo this, call RestoreCaret.
  virtual void SetCaret(nsCaret *aNewCaret) = 0;

   * Restore the caret to the original caret that this pres shell was created
   * with.
  virtual void RestoreCaret() = 0;

   * Should the images have borders etc.  Actual visual effects are determined
   * by the frames.  Visual effects may not effect layout, only display.
   * Takes effect on next repaint, does not force a repaint itself.
   * @param aInEnable  if true, visual selection effects are enabled
   *                   if false visual selection effects are disabled
  NS_IMETHOD SetSelectionFlags(int16_t aInEnable) = 0;

    * Gets the current state of non text selection effects
    * @return   current state of non text selection,
    *           as set by SetDisplayNonTextSelection
  int16_t GetSelectionFlags() const { return mSelectionFlags; }

  virtual mozilla::dom::Selection*
    GetCurrentSelection(mozilla::SelectionType aSelectionType) = 0;

   * Gets a selection controller for the focused content in the DOM window
   * for mDocument.
   * @param aFocusedContent     If there is focused content in the DOM window,
   *                            the focused content will be returned.  This may
   *                            be nullptr if it's not necessary.
   * @return                    A selection controller for focused content.
   *                            E.g., if an <input> element has focus, returns
   *                            the independent selection controller of it.
   *                            If the DOM window does not have focused content
   *                            (similar to Document.activeElement), returns
   *                            nullptr.
  virtual already_AddRefed<nsISelectionController>
              nsIContent** aFocusedContent = nullptr) = 0;

    * Interface to dispatch events via the presshell
    * @note The caller must have a strong reference to the PresShell.
  virtual nsresult HandleEventWithTarget(
                                 mozilla::WidgetEvent* aEvent,
                                 nsIFrame* aFrame,
                                 nsIContent* aContent,
                                 nsEventStatus* aStatus) = 0;

   * Dispatch event to content only (NOT full processing)
   * @note The caller must have a strong reference to the PresShell.
  virtual nsresult HandleDOMEventWithTarget(
                                 nsIContent* aTargetContent,
                                 mozilla::WidgetEvent* aEvent,
                                 nsEventStatus* aStatus) = 0;

   * Dispatch event to content only (NOT full processing)
   * @note The caller must have a strong reference to the PresShell.
  virtual nsresult HandleDOMEventWithTarget(nsIContent* aTargetContent,
                                                        nsIDOMEvent* aEvent,
                                                        nsEventStatus* aStatus) = 0;

   * Return whether or not the event is valid to be dispatched
  virtual bool CanDispatchEvent(
      const mozilla::WidgetGUIEvent* aEvent = nullptr) const = 0;

    * Gets the current target event frame from the PresShell
  virtual nsIFrame* GetEventTargetFrame() = 0;

    * Gets the current target event frame from the PresShell
  virtual already_AddRefed<nsIContent> GetEventTargetContent(
                                                     mozilla::WidgetEvent* aEvent) = 0;

   * Get and set the history state for the current document

  virtual nsresult CaptureHistoryState(nsILayoutHistoryState** aLayoutHistoryState) = 0;

   * Determine if reflow is currently locked
   * returns true if reflow is locked, false otherwise
  bool IsReflowLocked() const { return mIsReflowing; }

   * Called to find out if painting is suppressed for this presshell.  If it is suppressd,
   * we don't allow the painting of any layer but the background, and we don't
   * recur into our children.
  bool IsPaintingSuppressed() const { return mPaintingSuppressed; }

   * Pause painting by freezing the refresh driver of this and all parent
   * presentations. This may not have the desired effect if this pres shell
   * has its own refresh driver.
  virtual void PausePainting() = 0;

   * Resume painting by thawing the refresh driver of this and all parent
   * presentations. This may not have the desired effect if this pres shell
   * has its own refresh driver.
  virtual void ResumePainting() = 0;

   * Unsuppress painting.
  virtual void UnsuppressPainting() = 0;

   * Get the set of agent style sheets for this presentation
  virtual nsresult GetAgentStyleSheets(
      nsTArray<RefPtr<mozilla::StyleSheet>>& aSheets) = 0;

   * Replace the set of agent style sheets
  virtual nsresult SetAgentStyleSheets(
      const nsTArray<RefPtr<mozilla::StyleSheet>>& aSheets) = 0;

   * Add an override style sheet for this presentation
  virtual nsresult AddOverrideStyleSheet(mozilla::StyleSheet* aSheet) = 0;

   * Remove an override style sheet
  virtual nsresult RemoveOverrideStyleSheet(mozilla::StyleSheet* aSheet) = 0;

   * Reconstruct frames for all elements in the document
  virtual void ReconstructFrames() = 0;

   * Notify that a content node's state has changed
  virtual void ContentStateChanged(nsIDocument* aDocument,
                                   nsIContent* aContent,
                                   mozilla::EventStates aStateMask) = 0;

   * See if reflow verification is enabled. To enable reflow verification add
   * "verifyreflow:1" to your MOZ_LOG environment variable (any non-zero
   * debug level will work). Or, call SetVerifyReflowEnable with true.
  static bool GetVerifyReflowEnable();

   * Set the verify-reflow enable flag.
  static void SetVerifyReflowEnable(bool aEnabled);

  virtual nsIFrame* GetAbsoluteContainingBlock(nsIFrame* aFrame);

  virtual void DumpReflows() = 0;
  virtual void CountReflows(const char * aName, nsIFrame * aFrame) = 0;
  virtual void PaintCount(const char * aName,
                                      gfxContext* aRenderingContext,
                                      nsPresContext * aPresContext,
                                      nsIFrame * aFrame,
                                      const nsPoint& aOffset,
                                      uint32_t aColor) = 0;
  virtual void SetPaintFrameCount(bool aOn) = 0;
  virtual bool IsPaintingFrameCounts() = 0;

#ifdef DEBUG
  // Debugging hooks
  virtual void ListStyleContexts(FILE *out, int32_t aIndent = 0) = 0;

  virtual void ListStyleSheets(FILE *out, int32_t aIndent = 0) = 0;
  virtual void VerifyStyleTree() = 0;

   * Return true if accessibility is active.
  static bool IsAccessibilityActive();

   * Return accessibility service if accessibility is active.
  static nsAccessibilityService* AccService();

   * Stop all active elements (plugins and the caret) in this presentation and
   * in the presentations of subdocuments.  Resets painting to a suppressed state.
   * XXX this should include image animations
  virtual void Freeze() = 0;
  bool IsFrozen() { return mFrozen; }

   * Restarts active elements (plugins) in this presentation and in the
   * presentations of subdocuments, then do a full invalidate of the content area.
  virtual void Thaw() = 0;

  virtual void FireOrClearDelayedEvents(bool aFireEvents) = 0;

   * When this shell is disconnected from its containing docshell, we
   * lose our container pointer.  However, we'd still like to be able to target
   * user events at the docshell's parent.  This pointer allows us to do that.
   * It should not be used for any other purpose.
  void SetForwardingContainer(const mozilla::WeakPtr<nsDocShell> &aContainer);

   * Render the document into an arbitrary gfxContext
   * Designed for getting a picture of a document or a piece of a document
   * Note that callers will generally want to call FlushPendingNotifications
   * to get an up-to-date view of the document
   * @param aRect is the region to capture into the offscreen buffer, in the
   * root frame's coordinate system (if aIgnoreViewportScrolling is false)
   * or in the root scrolled frame's coordinate system
   * (if aIgnoreViewportScrolling is true). The coordinates are in appunits.
   * @param aFlags see below;
   *   set RENDER_IS_UNTRUSTED if the contents may be passed to malicious
   * agents. E.g. we might choose not to paint the contents of sensitive widgets
   * such as the file name in a file upload widget, and we might choose not
   * to paint themes.
   * clipping and scrollbar painting due to scrolling in the viewport
   *   set RENDER_CARET to draw the caret if one would be visible
   * (by default the caret is never drawn)
   *   set RENDER_USE_LAYER_MANAGER to force rendering to go through
   * the layer manager for the window. This may be unexpectedly slow
   * (if the layer manager must read back data from the GPU) or low-quality
   * (if the layer manager reads back pixel data and scales it
   * instead of rendering using the appropriate scaling). It may also
   * slow everything down if the area rendered does not correspond to the
   * normal visible area of the window.
   *   set RENDER_ASYNC_DECODE_IMAGES to avoid having images synchronously
   * decoded during rendering.
   * (by default images decode synchronously with RenderDocument)
   *   set RENDER_DOCUMENT_RELATIVE to render the document as if there has been
   * no scrolling and interpret |aRect| relative to the document instead of the
   * CSS viewport. Only considered if RENDER_IGNORE_VIEWPORT_SCROLLING is set
   * or the document is in ignore viewport scrolling mode
   * (nsIPresShell::SetIgnoreViewportScrolling/IgnoringViewportScrolling).
   * @param aBackgroundColor a background color to render onto
   * @param aRenderedContext the gfxContext to render to. We render so that
   * one CSS pixel in the source document is rendered to one unit in the current
   * transform.
  enum {
    RENDER_CARET = 0x04,
  virtual nsresult RenderDocument(const nsRect& aRect, uint32_t aFlags,
                                  nscolor aBackgroundColor,
                                  gfxContext* aRenderedContext) = 0;

  enum {
    RENDER_IS_IMAGE = 0x100,

   * Renders a node aNode to a surface and returns it. The aRegion may be used
   * to clip the rendering. This region is measured in CSS pixels from the
   * edge of the presshell area. The aPoint, aScreenRect and aFlags arguments
   * function in a similar manner as RenderSelection.
  virtual already_AddRefed<mozilla::gfx::SourceSurface>
  RenderNode(nsIDOMNode* aNode,
             nsIntRegion* aRegion,
             const mozilla::LayoutDeviceIntPoint aPoint,
             mozilla::LayoutDeviceIntRect* aScreenRect,
             uint32_t aFlags) = 0;

   * Renders a selection to a surface and returns it. This method is primarily
   * intended to create the drag feedback when dragging a selection.
   * aScreenRect will be filled in with the bounding rectangle of the
   * selection area on screen.
   * If the area of the selection is large and the RENDER_AUTO_SCALE flag is
   * set, the image will be scaled down. The argument aPoint is used in this
   * case as a reference point when determining the new screen rectangle after
   * scaling. Typically, this will be the mouse position, so that the screen
   * rectangle is positioned such that the mouse is over the same point in the
   * scaled image as in the original. When scaling does not occur, the mouse
   * point isn't used because the position can be determined from the displayed
   * frames.
  virtual already_AddRefed<mozilla::gfx::SourceSurface>
  RenderSelection(nsISelection* aSelection,
                  const mozilla::LayoutDeviceIntPoint aPoint,
                  mozilla::LayoutDeviceIntRect* aScreenRect,
                  uint32_t aFlags) = 0;

  void AddAutoWeakFrameInternal(AutoWeakFrame* aWeakFrame);
  virtual void AddAutoWeakFrameExternal(AutoWeakFrame* aWeakFrame);
  void AddWeakFrameInternal(WeakFrame* aWeakFrame);
  virtual void AddWeakFrameExternal(WeakFrame* aWeakFrame);

  void AddAutoWeakFrame(AutoWeakFrame* aWeakFrame)
  void AddWeakFrame(WeakFrame* aWeakFrame)

  void RemoveAutoWeakFrameInternal(AutoWeakFrame* aWeakFrame);
  virtual void RemoveAutoWeakFrameExternal(AutoWeakFrame* aWeakFrame);
  void RemoveWeakFrameInternal(WeakFrame* aWeakFrame);
  virtual void RemoveWeakFrameExternal(WeakFrame* aWeakFrame);

  void RemoveAutoWeakFrame(AutoWeakFrame* aWeakFrame)
  void RemoveWeakFrame(WeakFrame* aWeakFrame)

#ifdef DEBUG
  nsIFrame* GetDrawEventTargetFrame() { return mDrawEventTargetFrame; }

   * Stop or restart non synthetic test mouse event handling on *all*
   * presShells.
   * @param aDisable If true, disable all non synthetic test mouse
   * events on all presShells.  Otherwise, enable them.
  virtual void DisableNonTestMouseEvents(bool aDisable) = 0;

   * Record the background color of the most recently drawn canvas. This color
   * is composited on top of the user's default background color and then used
   * to draw the background color of the canvas. See PresShell::Paint,
   * PresShell::PaintDefaultBackground, and nsDocShell::SetupNewViewer;
   * bug 488242, bug 476557 and other bugs mentioned there.
  void SetCanvasBackground(nscolor aColor) { mCanvasBackgroundColor = aColor; }
  nscolor GetCanvasBackground() { return mCanvasBackgroundColor; }

   * Use the current frame tree (if it exists) to update the background
   * color of the most recently drawn canvas.
  virtual void UpdateCanvasBackground() = 0;

   * Add a solid color item to the bottom of aList with frame aFrame and bounds
   * aBounds. Checks first if this needs to be done by checking if aFrame is a
   * canvas frame (if the FORCE_DRAW flag is passed then this check is skipped).
   * aBackstopColor is composed behind the background color of the canvas, it is
   * transparent by default.
   * We attempt to make the background color part of the scrolled canvas (to reduce
   * transparent layers), and if async scrolling is enabled (and the background
   * is opaque) then we add a second, unscrolled item to handle the checkerboarding
   * case.
   * ADD_FOR_SUBDOC shoud be specified when calling this for a subdocument, and
   * LayoutUseContainersForRootFrame might cause the whole list to be scrolled. In
   * that case the second unscrolled item will be elided.
   * APPEND_UNSCROLLED_ONLY only attempts to add the unscrolled item, so that we
   * can add it manually after LayoutUseContainersForRootFrame has built the
   * scrolling ContainerLayer.
  enum {
    FORCE_DRAW = 0x01,
    ADD_FOR_SUBDOC = 0x02,
  virtual void AddCanvasBackgroundColorItem(nsDisplayListBuilder& aBuilder,
                                            nsDisplayList& aList,
                                            nsIFrame* aFrame,
                                            const nsRect& aBounds,
                                            nscolor aBackstopColor = NS_RGBA(0,0,0,0),
                                            uint32_t aFlags = 0) = 0;

   * Add a solid color item to the bottom of aList with frame aFrame and
   * bounds aBounds representing the dark grey background behind the page of a
   * print preview presentation.
  virtual void AddPrintPreviewBackgroundItem(nsDisplayListBuilder& aBuilder,
                                             nsDisplayList& aList,
                                             nsIFrame* aFrame,
                                             const nsRect& aBounds) = 0;

   * Computes the backstop color for the view: transparent if in a transparent
   * widget, otherwise the PresContext default background color. This color is
   * only visible if the contents of the view as a whole are translucent.
  virtual nscolor ComputeBackstopColor(nsView* aDisplayRoot) = 0;

  void ObserveNativeAnonMutationsForPrint(bool aObserve)
    mObservesMutationsForPrint = aObserve;
  bool ObservesNativeAnonMutationsForPrint()
    return mObservesMutationsForPrint;

  virtual nsresult SetIsActive(bool aIsActive) = 0;

  bool IsActive()
    return mIsActive;

  // mouse capturing
  static CapturingContentInfo gCaptureInfo;

  class PointerCaptureInfo final
    nsCOMPtr<nsIContent> mPendingContent;
    nsCOMPtr<nsIContent> mOverrideContent;

    explicit PointerCaptureInfo(nsIContent* aPendingContent)
      : mPendingContent(aPendingContent)


    bool Empty()
      return !(mPendingContent || mOverrideContent);

  class PointerInfo final
    uint16_t mPointerType;
    bool mActiveState;
    bool mPrimaryState;
    bool mPreventMouseEventByContent;
    explicit PointerInfo(bool aActiveState, uint16_t aPointerType,
                         bool aPrimaryState)
      : mPointerType(aPointerType)
      , mActiveState(aActiveState)
      , mPrimaryState(aPrimaryState)
      , mPreventMouseEventByContent(false)

  static void DispatchGotOrLostPointerCaptureEvent(
                bool aIsGotCapture,
                const mozilla::WidgetPointerEvent* aPointerEvent,
                nsIContent* aCaptureTarget);

  static PointerCaptureInfo* GetPointerCaptureInfo(uint32_t aPointerId);
  static void SetPointerCapturingContent(uint32_t aPointerId,
                                         nsIContent* aContent);
  static void ReleasePointerCapturingContent(uint32_t aPointerId);
  static nsIContent* GetPointerCapturingContent(uint32_t aPointerId);

  // CheckPointerCaptureState checks cases, when got/lostpointercapture events
  // should be fired.
  static void CheckPointerCaptureState(
                const mozilla::WidgetPointerEvent* aPointerEvent);

  // GetPointerInfo returns true if pointer with aPointerId is situated in
  // device, false otherwise.
  // aActiveState is additional information, which shows state of pointer like
  // button state for mouse.
  static bool GetPointerInfo(uint32_t aPointerId, bool& aActiveState);

  // GetPointerType returns pointer type like mouse, pen or touch for pointer
  // event with pointerId
  static uint16_t GetPointerType(uint32_t aPointerId);

  // GetPointerPrimaryState returns state of attribute isPrimary for pointer
  // event with pointerId
  static bool GetPointerPrimaryState(uint32_t aPointerId);

   * When capturing content is set, it traps all mouse events and retargets
   * them at this content node. If capturing is not allowed
   * (gCaptureInfo.mAllowed is false), then capturing is not set. However, if
   * the CAPTURE_IGNOREALLOWED flag is set, the allowed state is ignored and
   * capturing is set regardless. To disable capture, pass null for the value
   * of aContent.
   * If CAPTURE_RETARGETTOELEMENT is set, all mouse events are targeted at
   * aContent only. Otherwise, mouse events are targeted at aContent or its
   * descendants. That is, descendants of aContent receive mouse events as
   * they normally would, but mouse events outside of aContent are retargeted
   * to aContent.
   * If CAPTURE_PREVENTDRAG is set then drags are prevented from starting while
   * this capture is active.
   * events are targeted at aContent, but capturing is held more strongly (i.e.,
   * calls to SetCapturingContent won't unlock unless CAPTURE_POINTERLOCK is
   * set again).
  static void SetCapturingContent(nsIContent* aContent, uint8_t aFlags);

   * Return the active content currently capturing the mouse if any.
  static nsIContent* GetCapturingContent()
    return gCaptureInfo.mContent;

   * Allow or disallow mouse capturing.
  static void AllowMouseCapture(bool aAllowed)
    gCaptureInfo.mAllowed = aAllowed;

   * Returns true if there is an active mouse capture that wants to prevent
   * drags.
  static bool IsMouseCapturePreventingDrag()
    return gCaptureInfo.mPreventDrag && gCaptureInfo.mContent;

   * Keep track of how many times this presshell has been rendered to
   * a window.
  uint64_t GetPaintCount() { return mPaintCount; }
  void IncrementPaintCount() { ++mPaintCount; }

   * Get the root DOM window of this presShell.
  virtual already_AddRefed<nsPIDOMWindowOuter> GetRootWindow() = 0;

   * This returns the focused DOM window under our top level window.
   * I.e., when we are deactive, this returns the *last* focused DOM window.
  virtual already_AddRefed<nsPIDOMWindowOuter> GetFocusedDOMWindowInOurWindow() = 0;

   * Get the layer manager for the widget of the root view, if it has
   * one.
  virtual LayerManager* GetLayerManager() = 0;

   * Return true iff there is a widget rendering this presShell and that
   * widget is APZ-enabled.
  virtual bool AsyncPanZoomEnabled() = 0;

   * Track whether we're ignoring viewport scrolling for the purposes
   * of painting.  If we are ignoring, then layers aren't clipped to
   * the CSS viewport and scrollbars aren't drawn.
  virtual void SetIgnoreViewportScrolling(bool aIgnore) = 0;
  bool IgnoringViewportScrolling() const

   * Set a "resolution" for the document, which if not 1.0 will
   * allocate more or fewer pixels for rescalable content by a factor
   * of |resolution| in both dimensions.  Return NS_OK iff the
   * resolution bounds are sane, and the resolution of this was
   * actually updated.
   * The resolution defaults to 1.0.
  virtual nsresult SetResolution(float aResolution) = 0;
  float GetResolution() const { return mResolution.valueOr(1.0); }
  virtual float GetCumulativeResolution() = 0;

   * Calculate the cumulative scale resolution from this document up to
   * but not including the root document.
  virtual float GetCumulativeNonRootScaleResolution() = 0;

   * Was the current resolution set by the user or just default initialized?
  bool IsResolutionSet() { return mResolution.isSome(); }

   * Similar to SetResolution() but also increases the scale of the content
   * by the same amount.
  virtual nsresult SetResolutionAndScaleTo(float aResolution) = 0;

   * Return whether we are scaling to the set resolution.
   * This is initially false; it's set to true by a call to
   * SetResolutionAndScaleTo(), and set to false by a call to SetResolution().
  virtual bool ScaleToResolution() const = 0;

   * Used by session restore code to restore a resolution before the first
   * paint.
  virtual void SetRestoreResolution(float aResolution,
                                    mozilla::LayoutDeviceIntSize aDisplaySize) = 0;

   * Returns whether we are in a DrawWindow() call that used the
  bool InDrawWindowNotFlushing() const
  { return mRenderFlags & STATE_DRAWWINDOW_NOT_FLUSHING; }

   * Set the isFirstPaint flag.
  void SetIsFirstPaint(bool aIsFirstPaint) { mIsFirstPaint = aIsFirstPaint; }

   * Get the isFirstPaint flag.
  bool GetIsFirstPaint() const { return mIsFirstPaint; }

  uint32_t GetPresShellId() { return mPresShellId; }

   * Get the APZ FocusTarget used for async keyboard scrolling.
  const FocusTarget& GetAPZFocusTarget() const { return mAPZFocusTarget; }

   * Dispatch a mouse move event based on the most recent mouse position if
   * this PresShell is visible. This is used when the contents of the page
   * moved (aFromScroll is false) or scrolled (aFromScroll is true).
  virtual void SynthesizeMouseMove(bool aFromScroll) = 0;

  enum PaintFlags {
    /* Update the layer tree and paint PaintedLayers. If this is not specified,
     * we may still have to do it if the layer tree lost PaintedLayer contents
     * we need for compositing. */
    PAINT_LAYERS = 0x01,
    /* Composite layers to the window. */
    /* Sync-decode images. */
  virtual void Paint(nsView* aViewToPaint, const nsRegion& aDirtyRegion,
                     uint32_t aFlags) = 0;
  virtual nsresult HandleEvent(nsIFrame* aFrame,
                               mozilla::WidgetGUIEvent* aEvent,
                               bool aDontRetargetEvents,
                               nsEventStatus* aEventStatus,
                               nsIContent** aTargetContent = nullptr) = 0;
  virtual bool ShouldIgnoreInvalidation() = 0;
   * Notify that we're going to call Paint with PAINT_LAYERS
   * on the pres shell for a widget (which might not be this one, since
   * WillPaint is called on all presshells in the same toplevel window as the
   * painted widget). This is issued at a time when it's safe to modify
   * widget geometry.
  virtual void WillPaint() = 0;
   * Notify that we're going to call Paint with PAINT_COMPOSITE.
   * Fires on the presshell for the painted widget.
   * This is issued at a time when it's safe to modify widget geometry.
  virtual void WillPaintWindow() = 0;
   * Notify that we called Paint with PAINT_COMPOSITE.
   * Fires on the presshell for the painted widget.
   * This is issued at a time when it's safe to modify widget geometry.
  virtual void DidPaintWindow() = 0;

   * Ensures that the refresh driver is running, and schedules a view
   * manager flush on the next tick.
   * @param aType PAINT_DELAYED_COMPRESS : Schedule a paint to be executed after a delay, and
   * put FrameLayerBuilder in 'compressed' mode that avoids short cut optimizations.
  enum PaintType {
  virtual void ScheduleViewManagerFlush(PaintType aType = PAINT_DEFAULT) = 0;
  virtual void ClearMouseCaptureOnView(nsView* aView) = 0;
  virtual bool IsVisible() = 0;
  virtual void DispatchSynthMouseMove(mozilla::WidgetGUIEvent* aEvent,
                                      bool aFlushOnHoverChange) = 0;

  virtual void AddSizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf,
                                      nsArenaMemoryStats* aArenaObjectsSize,
                                      size_t* aPresShellSize,
                                      size_t* aStyleSetsSize,
                                      size_t* aTextRunsSize,
                                      size_t* aPresContextSize,
                                      size_t* aFramePropertiesSize) = 0;

   * Methods that retrieve the cached font inflation preferences.
  uint32_t FontSizeInflationEmPerLine() const {
    return mFontSizeInflationEmPerLine;

  uint32_t FontSizeInflationMinTwips() const {
    return mFontSizeInflationMinTwips;

  uint32_t FontSizeInflationLineThreshold() const {
    return mFontSizeInflationLineThreshold;

  bool FontSizeInflationForceEnabled() const {
    return mFontSizeInflationForceEnabled;

  bool FontSizeInflationDisabledInMasterProcess() const {
    return mFontSizeInflationDisabledInMasterProcess;

   * Determine if font size inflation is enabled. This value is cached until
   * it becomes dirty.
   * @returns true, if font size inflation is enabled; false otherwise.
  bool FontSizeInflationEnabled();

   * Notify the pres shell that an event occurred making the current value of
   * mFontSizeInflationEnabled invalid. This will schedule a recomputation of
   * whether font size inflation is enabled on the next call to
   * FontSizeInflationEnabled().
  void NotifyFontSizeInflationEnabledIsDirty()
    mFontSizeInflationEnabledIsDirty = true;

  // Approximate frame visibility tracking public API.

  /// Schedule an update of the list of approximately visible frames "soon".
  /// This lets the refresh driver know that we want a visibility update in the
  /// near future. The refresh driver applies its own heuristics and throttling
  /// to decide when to actually perform the visibility update.
  virtual void ScheduleApproximateFrameVisibilityUpdateSoon() = 0;

  /// Schedule an update of the list of approximately visible frames "now". The
  /// update runs asynchronously, but it will be posted to the event loop
  /// immediately. Prefer the "soon" variation of this method when possible, as
  /// this variation ignores the refresh driver's heuristics.
  virtual void ScheduleApproximateFrameVisibilityUpdateNow() = 0;

  /// Clears the current list of approximately visible frames on this pres shell
  /// and replaces it with frames that are in the display list @aList.
  virtual void RebuildApproximateFrameVisibilityDisplayList(const nsDisplayList& aList) = 0;
  virtual void RebuildApproximateFrameVisibility(nsRect* aRect = nullptr,
                                                 bool aRemoveOnly = false) = 0;

  /// Ensures @aFrame is in the list of approximately visible frames.
  virtual void EnsureFrameInApproximatelyVisibleList(nsIFrame* aFrame) = 0;

  /// Removes @aFrame from the list of approximately visible frames if present.
  virtual void RemoveFrameFromApproximatelyVisibleList(nsIFrame* aFrame) = 0;

  /// Whether we should assume all frames are visible.
  virtual bool AssumeAllFramesVisible() = 0;

   * Returns whether the document's style set's rule processor for the
   * specified level of the cascade is shared by multiple style sets.
   * @param aSheetType One of the nsIStyleSheetService.*_SHEET constants.
  nsresult HasRuleProcessorUsedByMultipleStyleSets(uint32_t aSheetType,
                                                   bool* aRetVal);

   * Refresh observer management.
  virtual bool AddRefreshObserverExternal(nsARefreshObserver* aObserver,
                                          mozilla::FlushType aFlushType);
  bool AddRefreshObserverInternal(nsARefreshObserver* aObserver,
                                  mozilla::FlushType aFlushType);
  virtual bool RemoveRefreshObserverExternal(nsARefreshObserver* aObserver,
                                             mozilla::FlushType aFlushType);
  bool RemoveRefreshObserverInternal(nsARefreshObserver* aObserver,
                                     mozilla::FlushType aFlushType);

  void DoObserveStyleFlushes();
  void DoObserveLayoutFlushes();

   * Do computations necessary to determine if font size inflation is enabled.
   * This value is cached after computation, as the computation is somewhat
   * expensive.
  void RecomputeFontSizeInflationEnabled();

   * Does the actual work of figuring out the current state of font size inflation.
  bool DetermineFontSizeInflationState();

   * Apply the system font scale from the corresponding pref to the PresContext,
   * taking into account the current state of font size inflation.
  void HandleSystemFontScale();

  void RecordAlloc(void* aPtr) {
#ifdef DEBUG

  void RecordFree(void* aPtr) {
#ifdef DEBUG

  bool AddRefreshObserver(nsARefreshObserver* aObserver,
                          mozilla::FlushType aFlushType) {
    return AddRefreshObserverInternal(aObserver, aFlushType);
    return AddRefreshObserverExternal(aObserver, aFlushType);

  bool RemoveRefreshObserver(nsARefreshObserver* aObserver,
                             mozilla::FlushType aFlushType) {
    return RemoveRefreshObserverInternal(aObserver, aFlushType);
    return RemoveRefreshObserverExternal(aObserver, aFlushType);

  virtual bool AddPostRefreshObserver(nsAPostRefreshObserver* aObserver);
  virtual bool RemovePostRefreshObserver(nsAPostRefreshObserver* aObserver);

   * Initialize and shut down static variables.
  static void InitializeStatics();
  static void ReleaseStatics();

  // If a frame in the subtree rooted at aFrame is capturing the mouse then
  // clears that capture.
  static void ClearMouseCapture(nsIFrame* aFrame);

  void SetScrollPositionClampingScrollPortSize(nscoord aWidth, nscoord aHeight);
  bool IsScrollPositionClampingScrollPortSizeSet() {
    return mScrollPositionClampingScrollPortSizeSet;
  nsSize GetScrollPositionClampingScrollPortSize() {
    NS_ASSERTION(mScrollPositionClampingScrollPortSizeSet, "asking for scroll port when its not set?");
    return mScrollPositionClampingScrollPortSize;

  virtual void WindowSizeMoveDone() = 0;
  virtual void SysColorChanged() = 0;
  virtual void ThemeChanged() = 0;
  virtual void BackingScaleFactorChanged() = 0;

   * Documents belonging to an invisible DocShell must not be painted ever.
  bool IsNeverPainting() {
    return mIsNeverPainting;

  void SetNeverPainting(bool aNeverPainting) {
    mIsNeverPainting = aNeverPainting;

  bool HasPendingReflow() const
    { return mObservingLayoutFlushes || mReflowContinueTimer; }

  void SyncWindowProperties(nsView* aView);

  virtual nsIDocument* GetPrimaryContentDocument() = 0;

  // aSheetType is one of the nsIStyleSheetService *_SHEET constants.
  virtual void NotifyStyleSheetServiceSheetAdded(mozilla::StyleSheet* aSheet,
                                                 uint32_t aSheetType) = 0;
  virtual void NotifyStyleSheetServiceSheetRemoved(mozilla::StyleSheet* aSheet,
                                                   uint32_t aSheetType) = 0;

  friend class nsRefreshDriver;

  // IMPORTANT: The ownership implicit in the following member variables
  // has been explicitly checked.  If you add any members to this class,
  // please make the ownership explicit (pinkerton, scc).

  // These are the same Document and PresContext owned by the DocViewer.
  // we must share ownership.
  nsCOMPtr<nsIDocument>     mDocument;
  RefPtr<nsPresContext>   mPresContext;
  mozilla::StyleSetHandle   mStyleSet;      // [OWNS]
  nsCSSFrameConstructor*    mFrameConstructor; // [OWNS]
  nsViewManager*           mViewManager;   // [WEAK] docViewer owns it so I don't have to
  nsPresArena               mFrameArena;
  RefPtr<nsFrameSelection> mSelection;
  // Pointer into mFrameConstructor - this is purely so that FrameManager() and
  // GetRootFrame() can be inlined:
  nsFrameManagerBase*       mFrameManager;
  mozilla::WeakPtr<nsDocShell>                 mForwardingContainer;
  mozilla::a11y::DocAccessible* mDocAccessible;

  // At least on Win32 and Mac after interupting a reflow we need to post
  // the resume reflow event off a timer to avoid event starvation because
  // posted messages are processed before other messages when the modal
  // moving/sizing loop is running, see bug 491700 for details.
  nsCOMPtr<nsITimer>        mReflowContinueTimer;

#ifdef DEBUG
  nsIFrame*                 mDrawEventTargetFrame;

  // We track allocated pointers in a debug-only hashtable to assert against
  // missing/double frees.
  nsTHashtable<nsPtrHashKey<void>> mAllocatedPointers;

  // Count of the number of times this presshell has been painted to a window.
  uint64_t                  mPaintCount;

  nsSize                    mScrollPositionClampingScrollPortSize;

  // A list of stack weak frames. This is a pointer to the last item in the list.
  AutoWeakFrame*            mAutoWeakFrames;

  // A hash table of heap allocated weak frames.
  nsTHashtable<nsPtrHashKey<WeakFrame>> mWeakFrames;

  // Most recent canvas background color.
  nscolor                   mCanvasBackgroundColor;

  // Used to force allocation and rendering of proportionally more or
  // less pixels in both dimensions.
  mozilla::Maybe<float>     mResolution;

  int16_t                   mSelectionFlags;

  // Flags controlling how our document is rendered.  These persist
  // between paints and so are tied with retained layer pixels.
  // PresShell flushes retained layers when the rendering state
  // changes in a way that prevents us from being able to (usefully)
  // re-use old pixels.
  RenderFlags               mRenderFlags;
  bool                      mDidInitialize : 1;
  bool                      mIsDestroying : 1;
  bool                      mIsReflowing : 1;

  // For all documents we initially lock down painting.
  bool                      mPaintingSuppressed : 1;

  bool                      mIsActive : 1;
  bool                      mFrozen : 1;
  bool                      mIsFirstPaint : 1;
  bool                      mObservesMutationsForPrint : 1;

  bool                      mSuppressInterruptibleReflows : 1;
  bool                      mScrollPositionClampingScrollPortSizeSet : 1;

  // True if a layout flush might not be a no-op
  bool mNeedLayoutFlush : 1;

  // True if a style flush might not be a no-op
  bool mNeedStyleFlush : 1;

  // True if we're observing the refresh driver for style flushes.
  bool mObservingStyleFlushes: 1;

  // True if we're observing the refresh driver for layout flushes, that is, if
  // we have a reflow scheduled.
  // Guaranteed to be false if mReflowContinueTimer is non-null.
  bool mObservingLayoutFlushes: 1;

  // True if there are throttled animations that would be processed when
  // performing a flush with mFlushAnimations == true.
  bool mNeedThrottledAnimationFlush : 1;

  uint32_t                  mPresShellId;

  // The focus sequence number of the last processed input event
  uint64_t                  mAPZFocusSequenceNumber;
  // The focus information needed for async keyboard scrolling
  FocusTarget               mAPZFocusTarget;

  static nsIContent*        gKeyDownTarget;

  // Cached font inflation values. This is done to prevent changing of font
  // inflation until a page is reloaded.
  uint32_t mFontSizeInflationEmPerLine;
  uint32_t mFontSizeInflationMinTwips;
  uint32_t mFontSizeInflationLineThreshold;
  bool mFontSizeInflationForceEnabled;
  bool mFontSizeInflationDisabledInMasterProcess;
  bool mFontSizeInflationEnabled;

  // Dirty bit indicating that mFontSizeInflationEnabled needs to be recomputed.
  bool mFontSizeInflationEnabledIsDirty;

  bool mPaintingIsFrozen;

  // If a document belongs to an invisible DocShell, this flag must be set
  // to true, so we can avoid any paint calls for widget related to this
  // presshell.
  bool mIsNeverPainting;

  // Whether we're currently under a FlushPendingNotifications.
  // This is used to handle flush reentry correctly.
  bool mInFlush;


#endif /* nsIPresShell_h___ */