Preserve fractional scroll offset for JS scrolling API

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 247 matching lines @@
 
     // NOTE: Only called from the ScrollAnimator.
     friend class ScrollAnimator;
     void setScrollOffsetFromAnimation(const DoublePoint&);
 
     // This function should be overriden by subclasses to perform the actual
     // scroll of the content. By default the DoublePoint version will just
     // call into the IntPoint version. If fractional scroll is needed, one
     // can override the DoublePoint version to take advantage of the double
     // precision scroll offset.
-    // FIXME: Remove the IntPoint version. crbug.com/414283.
+    // FIXME: Remove the IntPoint version. And change the function to
+    // take DoubleSize. crbug.com/414283.
     virtual void setScrollOffset(const IntPoint&) = 0;
     virtual void setScrollOffset(const DoublePoint& offset)
     {
         setScrollOffset(flooredIntPoint(offset));
     }
 
     virtual int lineStep(ScrollbarOrientation) const;
     virtual int pageStep(ScrollbarOrientation) const;
     virtual int documentStep(ScrollbarOrientation) const;
     virtual float pixelStep(ScrollbarOrientation) const;
@@ skipping 29 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