Merge 120750 - Fix scrollbar layers being misplaced with a clipped owner layer

Source/WebCore/rendering/RenderLayerBacking.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 226 matching lines @@
     for (RenderLayer* curr = layer; curr; curr = curr->parent()) {
         if (curr->hasTransform())
             return true;
     }
     
     return false;
 }
 
 bool RenderLayerBacking::shouldClipCompositedBounds() const
 {
+    // Scrollbar layers use this layer for relative positioning, so don't clip.
+    if (layerForHorizontalScrollbar() || layerForVerticalScrollbar())
+        return false;
+
     if (m_usingTiledCacheLayer)
         return true;
 
     if (!compositor()->compositingConsultsOverlap())
         return false;
 
     if (layerOrAncestorIsTransformed(m_owningLayer))
         return false;
 
     return true;
@@ skipping 1319 matching lines @@
 
     if (m_layerForScrollCorner)
         backingArea += m_layerForScrollCorner->backingStoreArea();
     
     return backingArea;
 }
 
 } // namespace WebCore
 
 #endif // USE(ACCELERATED_COMPOSITING)