RenderLayer::clipParent() should avoid calling clippedByAncestor unless needed

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 1662 matching lines @@
     for (RenderLayer* ancestor = parent(); ancestor && ancestor != scrollParent; ancestor = ancestor->parent()) {
         if (ancestor->stackingNode()->isStackingContainer())
             return 0;
     }
 
     return scrollParent;
 }
 
 RenderLayer* RenderLayer::clipParent() const
 {
-    const bool needsAncestorClip = compositor()->clippedByAncestor(this);
-
-    RenderLayer* clipParent = 0;
-    if ((compositingReasons() & CompositingReasonOutOfFlowClipping) && !needsAncestorClip) {
+    if (compositingReasons() & CompositingReasonOutOfFlowClipping && !compositor()->clippedByAncestor(this)) {
         if (RenderObject* containingBlock = renderer()->containingBlock())
-            clipParent = containingBlock->enclosingLayer()->enclosingCompositingLayer();
+            return containingBlock->enclosingLayer()->enclosingCompositingLayer();
     }
-
-    return clipParent;
+    return 0;
 }
 
 void RenderLayer::didUpdateNeedsCompositedScrolling()
 {
     m_stackingNode->updateIsNormalFlowOnly();
     updateSelfPaintingLayer();
 
     if (m_stackingNode->isStackingContainer())
         m_stackingNode->dirtyZOrderLists();
     else
@@ skipping 2331 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif