Use full mapLocalToAncestor machinery in ScrollingCoordinator.

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 228 matching lines @@
   virtual int visibleHeight() const { return visibleContentRect().height(); }
   virtual int visibleWidth() const { return visibleContentRect().width(); }
   virtual IntSize contentsSize() const = 0;
   virtual IntPoint lastKnownMousePosition() const { return IntPoint(); }
 
   virtual bool shouldSuspendScrollAnimations() const { return true; }
   virtual void scrollbarStyleChanged() {}
   virtual bool scrollbarsCanBeActive() const = 0;
 
   // Returns the bounding box of this scrollable area, in the coordinate system
-  // of the enclosing scroll view.
+  // of the top-level FrameView.
   virtual IntRect scrollableAreaBoundingBox() const = 0;
 
   virtual bool scrollAnimatorEnabled() const { return false; }
 
   // NOTE: Only called from Internals for testing.
   void updateScrollOffsetFromInternals(const IntSize&);
 
   IntSize clampScrollOffset(const IntSize&) const;
   ScrollOffset clampScrollOffset(const ScrollOffset&) const;
 
@@ skipping 186 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