Get rid of compositing and squashing helper methods on RenderLayerModelObject.

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 342 matching lines @@
     if (!context.usesCache()) {
         parentClipper.calculateClipRects(context, clipRects);
         return;
     }
 
     clipRects = *parentClipper.updateClipRects(context);
 }
 
 RenderLayer* RenderLayerClipper::clippingRootForPainting() const
 {
-    if (m_renderer.hasCompositedLayerMapping() || m_renderer.groupedMapping())
-        return const_cast<RenderLayer*>(m_renderer.layer());
+    const RenderLayer* current = m_renderer.layer();
+    // FIXME: getting rid of current->hasCompositedLayerMapping() here breaks the
+    // compositing/backing/no-backing-for-clip.html layout test, because there is a
+    // "composited but paints into ancestor" layer involved. However, it doesn't make sense that
+    // that check would be appropriate here but not inside the while loop below.
+    if (current->isPaintInvalidationContainer() || current->hasCompositedLayerMapping())
+        return const_cast<RenderLayer*>(current);
 
-    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) || current->groupedMapping())
+        if (current->transform() || current->isPaintInvalidationContainer())
             return const_cast<RenderLayer*>(current);
     }
 
     ASSERT_NOT_REACHED();
     return 0;
 }
 
 } // namespace WebCore