Disable scroll anchoring if the user engages in a drag motion

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 270 matching lines @@
     // Returns true if the scroller adjusts the scroll position to compensate
     // for layout movements (bit.ly/scroll-anchoring).
     virtual bool shouldPerformScrollAnchoring() const { return false; }
 
     // Need to promptly let go of owned animator objects.
     EAGERLY_FINALIZE();
     DECLARE_VIRTUAL_TRACE();
 
     virtual void clearScrollAnimators();
 
+    virtual void setUserMayHaveDragged(bool dragged) {};
+
 protected:
     ScrollableArea();
 
     ScrollbarOrientation scrollbarOrientationFromDirection(ScrollDirectionPhysical) const;
     float scrollStep(ScrollGranularity, ScrollbarOrientation) const;
 
     void setScrollOrigin(const IntPoint&);
     void resetScrollOriginChanged() { m_scrollOriginChanged = false; }
 
     // Needed to let the animators call scrollPositionChanged.
@@ skipping 41 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