Tie scroll anchoring adjustments to frame lifecycle instead of layout.

third_party/WebKit/Source/platform/scroll/ScrollTypes.h

 /*
  * Copyright (C) 2006 Apple Computer, 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 41 matching lines @@
   ScrollBlockDirectionForward,
   ScrollInlineDirectionBackward,
   ScrollInlineDirectionForward
 };
 
 enum ScrollDirectionPhysical { ScrollUp, ScrollDown, ScrollLeft, ScrollRight };
 
 enum ScrollType {
   UserScroll,
   ProgrammaticScroll,
+  ClampingScroll,
   CompositorScroll,
   AnchoringScroll
 };
 
 // Convert logical scroll direction to physical. Physical scroll directions are
 // unaffected.
 inline ScrollDirectionPhysical toPhysicalDirection(ScrollDirection direction,
                                                    bool isVertical,
                                                    bool isFlipped) {
   switch (direction) {
@@ skipping 165 matching lines @@
 
   return (dir == ScrollLeft || dir == ScrollRight) ? ScrollOffset(delta, 0)
                                                    : ScrollOffset(0, delta);
 }
 
 typedef unsigned ScrollbarControlPartMask;
 
 }  // namespace blink
 
 #endif