Bug 1405832 - part 1: ContentCacheInParent::RequestIMEToCommitComposition() should increment mPendingEventsNeedingAck itself if it treat the request handled synchronously without actually requesting IME to commit composition r=m_kato This is a simple bug of ContentCacheInParent. When ContentCacheInParent::RequestIMEToCommitComposition() returns true, PuppetWidget::RequestIMEToCommitComposition() will send eCompositionCommitRequestHandled pseudo event message back to the main process. This causes counting down mPendingEventsNeedingAck in ContentCacheInParent::OnEventNeedingAckHandled(). Therefore, in the normal path, ContentCacheInParent::OnCompositionEvent() increments it for receiving the pseudo event message. However, if the tab parent has already lost focus, RequestIMEToCommitComposition() returns true without requesting native IME to commit composition. So, ContentCacheInParent::OnCompositionEvent() cannot increment mPendingEventsNeedingAck for coming eCompositionCommitRequestHandled. Therefore, RequestIMEToCommitComposition() needs to increment mPendingEventsNeedingAck by itself when it won't request IME to commit composition but it returns true. MozReview-Commit-ID: 4Alwfy8avB

--- a/widget/ContentCache.cpp
+++ b/widget/ContentCache.cpp
@@ -1318,16 +1318,21 @@ ContentCacheInParent::RequestIMEToCommit
     // Use the latest composition string which may not be handled in the
     // remote process for avoiding data loss.
 #ifdef MOZ_CRASHREPORTER
     mRequestIMEToCommitCompositionResults.
       AppendElement(RequestIMEToCommitCompositionResult::
                       eReceivedAfterTabParentBlur);
 #endif // #ifdef MOZ_CRASHREPORTER
     aCommittedString = mCompositionString;
+    // After we return true from here, i.e., without actually requesting IME
+    // to commit composition, we will receive eCompositionCommitRequestHandled
+    // pseudo event message from the remote process.  So, we need to increment
+    // mPendingEventsNeedingAck here.
+    mPendingEventsNeedingAck++;
     return true;
   }
 
   RefPtr<TextComposition> composition =
     IMEStateManager::GetTextCompositionFor(aWidget);
   if (NS_WARN_IF(!composition)) {
     MOZ_LOG(sContentCacheLog, LogLevel::Warning,
       ("  0x%p RequestToCommitComposition(), "