Move the Widget hierarchy to the Oilpan heap.

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 264 matching lines @@
     virtual int lineStep(ScrollbarOrientation) const;
     virtual int pageStep(ScrollbarOrientation) const;
     virtual int documentStep(ScrollbarOrientation) const;
     virtual float pixelStep(ScrollbarOrientation) const;
 
     // Stores the paint invalidations for the scrollbars during layout.
     IntRect m_horizontalBarDamage;
     IntRect m_verticalBarDamage;
 
     struct ScrollableAreaAnimators {
-        OwnPtr<ScrollAnimator> scrollAnimator;
+        RefPtr<ScrollAnimator> scrollAnimator;
         OwnPtr<ProgrammaticScrollAnimator> programmaticScrollAnimator;
     };
 
     mutable OwnPtr<ScrollableAreaAnimators> m_animators;
     unsigned m_constrainsScrollingToContentEdge : 1;
 
     unsigned m_inLiveResize : 1;
 
     unsigned m_verticalScrollElasticity : 2; // ScrollElasticity
     unsigned m_horizontalScrollElasticity : 2; // ScrollElasticity
@@ skipping 12 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