Avoid N^2 walk placing renderers when building the render tree

Source/core/dom/shadow/ShadowRoot.cpp

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 130 matching lines @@
 
     StyleResolver* styleResolver = document()->styleResolver();
     styleResolver->pushParentShadowRoot(this);
 
     // When we're set to lazyAttach we'll have a FullStyleChange and we'll need
     // to promote the change to a Force for all our descendants so they get a
     // recalc and will attach.
     if (styleChangeType() == FullStyleChange)
         change = Force;
 
-    for (Node* child = firstChild(); child; child = child->nextSibling()) {
+    for (Node* child = lastChild(); child; child = child->previousSibling()) {
         if (child->isElementNode())
             toElement(child)->recalcStyle(change);
         else if (child->isTextNode())
             toText(child)->recalcTextStyle(change);
     }
 
     styleResolver->popParentShadowRoot(this);
     clearNeedsStyleRecalc();
     clearChildNeedsStyleRecalc();
 }
@@ skipping 115 matching lines @@
 {
     MemoryClassInfo info(memoryObjectInfo, this, WebCoreMemoryTypes::DOM);
     DocumentFragment::reportMemoryUsage(memoryObjectInfo);
     TreeScope::reportMemoryUsage(memoryObjectInfo);
     info.addMember(m_prev, "prev");
     info.addMember(m_next, "next");
     info.addMember(m_scopeDistribution, "scopeDistribution");
 }
 
 }