Update scroll parent correctly for squashing layers.

Source/core/rendering/RenderLayerClipper.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 343 matching lines @@
         parentClipper.calculateClipRects(clipRectsContext, clipRects);
         return;
     }
 
     parentClipper.updateClipRects(clipRectsContext);
     clipRects = *parentClipper.clipRects(clipRectsContext);
 }
 
 RenderLayer* RenderLayerClipper::clippingRootForPainting() const
 {
-    if (m_renderer->hasCompositedLayerMapping())
+    if (m_renderer->hasCompositedLayerMapping() || m_renderer->groupedMapping())
         return const_cast<RenderLayer*>(m_renderer->layer());
 
     const RenderLayer* current = m_renderer->layer();
     while (current) {
         if (current->isRootLayer())
             return const_cast<RenderLayer*>(current);
 
         current = current->compositingContainer();
         ASSERT(current);
-        if (current->transform()
-            || (current->compositingState() == PaintsIntoOwnBacking)
-        )
+        if (current->transform() || (current->compositingState() == PaintsIntoOwnBacking) || current->groupedMapping())
             return const_cast<RenderLayer*>(current);
     }
 
     ASSERT_NOT_REACHED();
     return 0;
 }
 
 } // namespace WebCore