Tie scroll anchoring adjustments to frame lifecycle instead of layout.

third_party/WebKit/Source/core/layout/LayoutBlock.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc.
  *               All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 381 matching lines @@
 }
 
 void LayoutBlock::layout() {
   DCHECK(!getScrollableArea() || getScrollableArea()->scrollAnchor());
 
   LayoutAnalyzer::Scope analyzer(*this);
 
   bool needsScrollAnchoring =
       hasOverflowClip() && getScrollableArea()->shouldPerformScrollAnchoring();
   if (needsScrollAnchoring)
-    getScrollableArea()->scrollAnchor()->save();
+    getScrollableArea()->scrollAnchor()->notifyBeforeLayout();
 
   // Table cells call layoutBlock directly, so don't add any logic here.  Put
   // code into layoutBlock().
   layoutBlock(false);
 
   // It's safe to check for control clip here, since controls can never be table
   // cells. If we have a lightweight clip, there can never be any overflow from
   // children.
   if (hasControlClip() && m_overflow)
     clearLayoutOverflow();
 
   invalidateBackgroundObscurationStatus();
-
-  // If clamping is delayed, we will restore in
-  // PaintLayerScrollableArea::clampScrollPositionsAfterLayout.
-  // Restoring during the intermediate layout may clamp the scroller to the
-  // wrong bounds.
-  bool clampingDelayed = PaintLayerScrollableArea::DelayScrollOffsetClampScope::
-      clampingIsDelayed();
-  if (needsScrollAnchoring && !clampingDelayed)
-    getScrollableArea()->scrollAnchor()->restore();
-
   m_heightAvailableToChildrenChanged = false;
 }
 
 bool LayoutBlock::widthAvailableToChildrenHasChanged() {
   // TODO(robhogan): Does m_widthAvailableToChildrenChanged always get reset
   // when it needs to?
   bool widthAvailableToChildrenHasChanged = m_widthAvailableToChildrenChanged;
   m_widthAvailableToChildrenChanged = false;
 
   // If we use border-box sizing, have percentage padding, and our parent has
@@ skipping 1777 matching lines @@
   }
 
   return availableHeight;
 }
 
 bool LayoutBlock::hasDefiniteLogicalHeight() const {
   return availableLogicalHeightForPercentageComputation() != LayoutUnit(-1);
 }
 
 }  // namespace blink