Remove mainthread overhang painting code

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 161 matching lines @@
     virtual DoublePoint scrollPositionDouble() const { return DoublePoint(scrollPosition()); }
     virtual IntPoint minimumScrollPosition() const = 0;
     virtual DoublePoint minimumScrollPositionDouble() const { return DoublePoint(minimumScrollPosition()); }
     virtual IntPoint maximumScrollPosition() const = 0;
     virtual DoublePoint maximumScrollPositionDouble() const { return DoublePoint(maximumScrollPosition()); }
 
     virtual IntRect visibleContentRect(IncludeScrollbarsInRect = ExcludeScrollbars) const;
     virtual int visibleHeight() const { return visibleContentRect().height(); }
     virtual int visibleWidth() const { return visibleContentRect().width(); }
     virtual IntSize contentsSize() const = 0;
-    virtual IntSize overhangAmount() const { return IntSize(); }
     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.
     virtual IntRect scrollableAreaBoundingBox() const = 0;
 
@@ skipping 126 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