Bug 1339891 part 2. Make FlushPendingNotifications on a presshell quickly no-op if there is nothing to flush. r=heycam

dom/base/nsDocument.cpp

@@ -7967,13 +7967,8 @@ nsDocument::FlushPendingNotifications(FlushType aType)
     mParentDocument->FlushPendingNotifications(parentType);
   }
 
-  // Call nsIPresShell::NeedFlush (inline, non-virtual) to check whether we
-  // really need to flush the shell (virtual, and needs a strong reference).
   if (nsIPresShell* shell = GetShell()) {
-    if (shell->NeedFlush(aType)) {
-      nsCOMPtr<nsIPresShell> presShell = shell;
-      presShell->FlushPendingNotifications(aType);
-    }
+    shell->FlushPendingNotifications(aType);
   }
 }
 

layout/base/PresShell.cpp

@@ -4065,7 +4065,7 @@ PresShell::IsSafeToFlush() const
 
 
 void
-PresShell::FlushPendingNotifications(FlushType aType)
+PresShell::DoFlushPendingNotifications(FlushType aType)
 {
   // by default, flush animations if aType >= FlushType::Style
   mozilla::ChangesToFlush flush(aType, aType >= FlushType::Style);
@@ -4073,7 +4073,7 @@ PresShell::FlushPendingNotifications(FlushType aType)
 }
 
 void
-PresShell::FlushPendingNotifications(mozilla::ChangesToFlush aFlush)
+PresShell::DoFlushPendingNotifications(mozilla::ChangesToFlush aFlush)
 {
   // Per our API contract, hold a strong ref to ourselves until we return.
   nsCOMPtr<nsIPresShell> kungFuDeathGrip = this;
@@ -4085,6 +4085,8 @@ PresShell::FlushPendingNotifications(mozilla::ChangesToFlush aFlush)
    */
   FlushType flushType = aFlush.mFlushType;
 
+  MOZ_ASSERT(NeedFlush(flushType), "Why did we get called?");
+
 #ifdef MOZ_GECKO_PROFILER
   static const EnumeratedArray<FlushType,
                                FlushType::Count,

layout/base/PresShell.h

@@ -126,8 +126,8 @@ public:
   virtual void FrameNeedsToContinueReflow(nsIFrame *aFrame) override;
   virtual void CancelAllPendingReflows() override;
   virtual bool IsSafeToFlush() const override;
-  virtual void FlushPendingNotifications(mozilla::FlushType aType) override;
-  virtual void FlushPendingNotifications(mozilla::ChangesToFlush aType) override;
+  virtual void DoFlushPendingNotifications(mozilla::FlushType aType) override;
+  virtual void DoFlushPendingNotifications(mozilla::ChangesToFlush aType) override;
   virtual void DestroyFramesFor(nsIContent*  aContent,
                                 nsIContent** aDestroyedFramesFor) override;
   virtual void CreateFramesFor(nsIContent* aContent) override;

layout/base/nsIPresShell.h

@@ -588,9 +588,33 @@ public:
    *
    * @param aType the type of notifications to flush
    */
-  virtual void FlushPendingNotifications(mozilla::FlushType aType) = 0;
-  virtual void FlushPendingNotifications(mozilla::ChangesToFlush aType) = 0;
+public:
+  void FlushPendingNotifications(mozilla::FlushType aType)
+  {
+    if (!NeedFlush(aType)) {
+      return;
+    }
 
+    DoFlushPendingNotifications(aType);
+  }
+
+  void FlushPendingNotifications(mozilla::ChangesToFlush aType)
+  {
+    if (!NeedFlush(aType.mFlushType)) {
+      return;
+    }
+
+    DoFlushPendingNotifications(aType);
+  }
+
+protected:
+  /**
+   * Implementation methods for FlushPendingNotifications.
+   */
+  virtual void DoFlushPendingNotifications(mozilla::FlushType aType) = 0;
+  virtual void DoFlushPendingNotifications(mozilla::ChangesToFlush aType) = 0;
+
+public:
   /**
    * Whether we might need a flush for the given flush type.  If this
    * function returns false, we definitely don't need to flush.