Fix paint invalidation rect tracking within composited scrolling layers.

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 100 matching lines @@
 bool LayoutBoxModelObject::hasAcceleratedCompositing() const
 {
     return view()->compositor()->hasAcceleratedCompositing();
 }
 
 LayoutBoxModelObject::LayoutBoxModelObject(ContainerNode* node)
     : LayoutObject(node)
 {
 }
 
+bool LayoutBoxModelObject::usesCompositedScrolling() const
+{
+    return hasOverflowClip() && hasLayer() && layer()->scrollableArea()->usesCompositedScrolling();
+}
+
 LayoutBoxModelObject::~LayoutBoxModelObject()
 {
     // Our layer should have been destroyed and cleared by now
     ASSERT(!hasLayer());
     ASSERT(!m_layer);
 }
 
 void LayoutBoxModelObject::willBeDestroyed()
 {
     ImageQualityController::remove(this);
@@ skipping 881 matching lines @@
     if (rootElementStyle->hasBackground())
         return false;
 
     if (node() != document().firstBodyElement())
         return false;
 
     return true;
 }
 
 } // namespace blink