Delete the Layer Squashing runtime feature.

Source/core/rendering/RenderLayer.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 2394 matching lines @@
 }
 
 CompositingState RenderLayer::compositingState() const
 {
     ASSERT(isAllowedToQueryCompositingState());
 
     // This is computed procedurally so there is no redundant state variable that
     // can get out of sync from the real actual compositing state.
 
     if (m_groupedMapping) {
-        ASSERT(compositor()->layerSquashingEnabled());
         ASSERT(!m_compositedLayerMapping);
         return PaintsIntoGroupedBacking;
     }
 
     if (!m_compositedLayerMapping)
         return NotComposited;
 
     return PaintsIntoOwnBacking;
 }
 
@@ skipping 450 matching lines @@
     }
 }
 
 void showLayerTree(const blink::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif