Implement overlay scrollbar fade out for non-composited scrollers.

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

 /*
  * Copyright (c) 2010, Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 88 matching lines @@
   virtual void contentAreaDidShow() const {}
   virtual void contentAreaDidHide() const {}
 
   virtual void finishCurrentScrollAnimations() {}
 
   virtual void didAddVerticalScrollbar(Scrollbar&) {}
   virtual void willRemoveVerticalScrollbar(Scrollbar&) {}
   virtual void didAddHorizontalScrollbar(Scrollbar&) {}
   virtual void willRemoveHorizontalScrollbar(Scrollbar&) {}
 
-  virtual bool shouldScrollbarParticipateInHitTesting(Scrollbar&) {
-    return true;
-  }
-
   virtual void notifyContentAreaScrolled(const ScrollOffset&) {}
 
   virtual bool setScrollbarsVisibleForTesting(bool) { return false; }
 
   DECLARE_VIRTUAL_TRACE();
 
  protected:
   explicit ScrollAnimatorBase(ScrollableArea*);
 
   virtual void notifyOffsetChanged();
 
   Member<ScrollableArea> m_scrollableArea;
 
   ScrollOffset m_currentOffset;
 };
 
 }  // namespace blink
 
 #endif  // ScrollAnimatorBase_h