Use ScrollAnchor in FrameView and PaintLayerScrollableArea.

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
  * License as published by the Free Software Foundation; either
@@ skipping 879 matching lines @@
         } else {
             layer()->scrollableArea()->updateAfterLayout();
         }
     }
 }
 
 void LayoutBlock::layout()
 {
     LayoutAnalyzer::Scope analyzer(*this);
 
+    bool needsScrollAnchoring = RuntimeEnabledFeatures::scrollAnchoringEnabled() && hasOverflowClip();
+    if (needsScrollAnchoring)
+        scrollableArea()->scrollAnchor().save();
+
     // 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 (needsScrollAnchoring)
+        scrollableArea()->scrollAnchor().restore();
 }
 
 bool LayoutBlock::widthAvailableToChildrenHasChanged()
 {
     bool widthAvailableToChildrenHasChanged = m_widthAvailableToChildrenChanged;
     m_widthAvailableToChildrenChanged = false;
 
     // If we use border-box sizing, have percentage padding, and our parent has changed width then the width available to our children has changed even
     // though our own width has remained the same.
     widthAvailableToChildrenHasChanged |= style()->boxSizing() == BORDER_BOX && needsPreferredWidthsRecalculation() && view()->layoutState()->containingBlockLogicalWidthChanged();
@@ skipping 1938 matching lines @@
 void LayoutBlock::showLineTreeAndMark(const InlineBox* markedBox1, const char* markedLabel1, const InlineBox* markedBox2, const char* markedLabel2, const LayoutObject* obj) const
 {
     showLayoutObject();
     for (const RootInlineBox* root = firstRootBox(); root; root = root->nextRootBox())
         root->showLineTreeAndMark(markedBox1, markedLabel1, markedBox2, markedLabel2, obj, 1);
 }
 
 #endif
 
 } // namespace blink