Blink Compositor Animation: Introduce CompositorAnimationHost correctly.

third_party/WebKit/Source/platform/scroll/ScrollableArea.h

 /*
  * Copyright (C) 2008, 2011 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 23 matching lines @@
 #include "platform/heap/Handle.h"
 #include "platform/scroll/ScrollAnimatorBase.h"
 #include "platform/scroll/ScrollTypes.h"
 #include "platform/scroll/Scrollbar.h"
 #include "wtf/MathExtras.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/Vector.h"
 
 namespace blink {
 
+class CompositorAnimationHost;
+class CompositorAnimationTimeline;
 class GraphicsLayer;
 class HostWindow;
 class LayoutBox;
 class LayoutObject;
 class PaintLayer;
 class ProgrammaticScrollAnimator;
 struct ScrollAlignment;
 class ScrollAnchor;
 class ScrollAnimatorBase;
 class CompositorAnimationTimeline;
@@ skipping 89 matching lines @@
   // yet.
   ScrollAnimatorBase* existingScrollAnimator() const {
     return m_scrollAnimator;
   }
 
   ProgrammaticScrollAnimator& programmaticScrollAnimator() const;
   ProgrammaticScrollAnimator* existingProgrammaticScrollAnimator() const {
     return m_programmaticScrollAnimator;
   }
 
+  virtual CompositorAnimationHost* compositorAnimationHost() const {
+    return nullptr;
+  }
   virtual CompositorAnimationTimeline* compositorAnimationTimeline() const {
     return nullptr;
   }
 
   // See Source/core/layout/README.md for an explanation of scroll origin.
   const IntPoint& scrollOrigin() const { return m_scrollOrigin; }
   bool scrollOriginChanged() const { return m_scrollOriginChanged; }
 
   // This is used to determine whether the incoming fractional scroll offset
   // should be truncated to integer. Current rule is that if
@@ skipping 277 matching lines @@
   // vertical-lr / ltr            NO                      NO
   // vertical-lr / rtl            NO                      YES
   // vertical-rl / ltr            YES                     NO
   // vertical-rl / rtl            YES                     YES
   IntPoint m_scrollOrigin;
 };
 
 }  // namespace blink
 
 #endif  // ScrollableArea_h