Don't automatically paint clipped backgrounds into scrolling contents layer.

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.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 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. 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 114 matching lines @@
     bool hasCustomScrollbars = false;
     // TODO(flackr): Detect opaque custom scrollbars which would cover up a border-box
     // background.
     if (PaintLayerScrollableArea* scrollableArea = getScrollableArea()) {
         if ((scrollableArea->horizontalScrollbar() && scrollableArea->horizontalScrollbar()->isCustomScrollbar())
             || (scrollableArea->verticalScrollbar() && scrollableArea->verticalScrollbar()->isCustomScrollbar())) {
             hasCustomScrollbars = true;
         }
     }
 
+    // TODO(flackr): When we correctly clip the scrolling contents layer we can
+    // paint locally equivalent backgrounds into it. https://crbug.com/645957
+    if (!style()->hasAutoClip())
+        return false;
+
     // TODO(flackr): We should be able to paint locally attached borders with a border-radius
     // but these currently do not paint correctly. https://crbug.com/645949
     if (style()->hasBorderRadius())
         return false;
 
     const FillLayer* layer = &(style()->backgroundLayers());
     for (; layer; layer = layer->next()) {
         if (layer->attachment() == LocalBackgroundAttachment)
             continue;
 
@@ skipping 1032 matching lines @@
     if (rootElementStyle->hasBackground())
         return false;
 
     if (node() != document().firstBodyElement())
         return false;
 
     return true;
 }
 
 } // namespace blink