RAL: Eliminate n^2 walk to find repaint containers

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 1090 matching lines @@
 
 const RenderLayer* RenderLayer::compositingContainer() const
 {
     if (stackingNode()->isNormalFlowOnly())
         return parent();
     if (RenderLayerStackingNode* ancestorStackingNode = stackingNode()->ancestorStackingContainerNode())
         return ancestorStackingNode->layer();
     return 0;
 }
 
+bool RenderLayer::isRepaintContainer() const
+{
+    return compositingState() == PaintsIntoOwnBacking || compositingState() == PaintsIntoGroupedBacking;
+}
+
 // FIXME: having two different functions named enclosingCompositingLayer and enclosingCompositingLayerForRepaint
 // is error-prone and misleading for reading code that uses these functions - especially compounded with
 // the includeSelf option. It is very likely that we don't even want either of these functions; A layer
 // should be told explicitly which GraphicsLayer is the repaintContainer for a RenderLayer, and
 // any other use cases should probably have an API between the non-compositing and compositing sides of code.
 RenderLayer* RenderLayer::enclosingCompositingLayer(IncludeSelfOrNot includeSelf) const
 {
     ASSERT(isAllowedToQueryCompositingState());
 
     if ((includeSelf == IncludeSelf) && compositingState() != NotComposited && compositingState() != PaintsIntoGroupedBacking)
         return const_cast<RenderLayer*>(this);
 
     for (const RenderLayer* curr = compositingContainer(); curr; curr = curr->compositingContainer()) {
         if (curr->compositingState() != NotComposited && curr->compositingState() != PaintsIntoGroupedBacking)
             return const_cast<RenderLayer*>(curr);
     }
 
     return 0;
 }
 
 RenderLayer* RenderLayer::enclosingCompositingLayerForRepaint(IncludeSelfOrNot includeSelf) const
 {
     ASSERT(isAllowedToQueryCompositingState());
 
-    if ((includeSelf == IncludeSelf) && (compositingState() == PaintsIntoOwnBacking || compositingState() == PaintsIntoGroupedBacking))
+    if ((includeSelf == IncludeSelf) && isRepaintContainer())
         return const_cast<RenderLayer*>(this);
 
     for (const RenderLayer* curr = compositingContainer(); curr; curr = curr->compositingContainer()) {
-        if (curr->compositingState() == PaintsIntoOwnBacking || curr->compositingState() == PaintsIntoGroupedBacking)
+        if (curr->isRepaintContainer())
             return const_cast<RenderLayer*>(curr);
     }
 
     return 0;
 }
 
 RenderLayer* RenderLayer::ancestorCompositedScrollingLayer() const
 {
     if (!compositor()->legacyOrCurrentAcceleratedCompositingForOverflowScrollEnabled())
         return 0;
@@ skipping 2870 matching lines @@
     }
 }
 
 void showLayerTree(const WebCore::RenderObject* renderer)
 {
     if (!renderer)
         return;
     showLayerTree(renderer->enclosingLayer());
 }
 #endif