Add a setting to do frame scrolls through the root layer.

Source/core/rendering/RenderBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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 249 matching lines @@
     toRenderGrid(parent())->dirtyGrid();
 }
 
 void RenderBox::updateFromStyle()
 {
     RenderBoxModelObject::updateFromStyle();
 
     RenderStyle* styleToUse = style();
     bool isRootObject = isDocumentElement();
     bool isViewObject = isRenderView();
+    bool rootLayerScrolls = document().settings() && document().settings()->rootLayerScrolls();
 
     // The root and the RenderView always paint their backgrounds/borders.
     if (isRootObject || isViewObject)
         setHasBoxDecorationBackground(true);
 
     setFloating(!isOutOfFlowPositioned() && styleToUse->isFloating());
 
     bool boxHasOverflowClip = false;
-    if (!styleToUse->isOverflowVisible() && isRenderBlock() && !isViewObject) {
+    if (!styleToUse->isOverflowVisible() && isRenderBlock() && (rootLayerScrolls || !isViewObject)) {
         // If overflow has been propagated to the viewport, it has no effect here.
         if (node() != document().viewportDefiningElement())
             boxHasOverflowClip = true;
     }
 
     if (boxHasOverflowClip != hasOverflowClip()) {
         // FIXME: This shouldn't be required if we tracked the visual overflow
         // generated by positioned children or self painting layers. crbug.com/345403
         for (RenderObject* child = slowFirstChild(); child; child = child->nextSibling())
             child->setMayNeedPaintInvalidation(true);
@@ skipping 4118 matching lines @@
     ASSERT(style()->hasBackground() || style()->hasBoxDecorations());
 
     if (m_rareData && m_rareData->m_previousBorderBoxSize.width() != -1)
         return m_rareData->m_previousBorderBoxSize;
 
     // We didn't save the old border box size because it was the same as the size of oldBounds.
     return previousBoundsSize;
 }
 
 } // namespace blink