Fix & clarify some comments in compositing. Rename clippedByAncestor to more accurately

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 1700 matching lines @@
             scrollParent = 0;
             break;
         }
     }
 
     return scrollParent;
 }
 
 RenderLayer* RenderLayer::clipParent() const
 {
-    if (compositingReasons() & CompositingReasonOutOfFlowClipping && !compositor()->clippedByAncestor(this)) {
+    if (compositingReasons() & CompositingReasonOutOfFlowClipping && !compositor()->clippedByNonAncestorInStackingTree(this)) {
         if (RenderObject* containingBlock = renderer()->containingBlock())
             return containingBlock->enclosingLayer()->enclosingCompositingLayer();
     }
     return 0;
 }
 
 void RenderLayer::didUpdateNeedsCompositedScrolling()
 {
     m_stackingNode->updateIsNormalFlowOnly();
     updateSelfPaintingLayer();
@@ skipping 2284 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif