Avoid calling markAncestorsWithChildNeedsStyleRecalc() constantly in childrenChanged

Source/core/dom/ContainerNode.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 636 matching lines @@
     clearChildNeedsStyleRecalc();
     Node::detach(context);
 }
 
 void ContainerNode::childrenChanged(bool changedByParser, Node*, Node*, int childCountDelta)
 {
     document().incDOMTreeVersion();
     if (!changedByParser && childCountDelta)
         document().updateRangesAfterChildrenChanged(this);
     invalidateNodeListCachesInAncestors();
-    if (childCountDelta > 0 && inActiveDocument()) {
+    if (childCountDelta > 0 && !childNeedsStyleRecalc()) {
         setChildNeedsStyleRecalc();
         markAncestorsWithChildNeedsStyleRecalc();
     }
 }
 
 void ContainerNode::cloneChildNodes(ContainerNode *clone)
 {
     TrackExceptionState exceptionState;
     for (Node* n = firstChild(); n && !exceptionState.hadException(); n = n->nextSibling())
         clone->appendChild(n->cloneNode(true), exceptionState);
@@ skipping 427 matching lines @@
         return true;
 
     if (node->isElementNode() && toElement(node)->shadow())
         return true;
 
     return false;
 }
 #endif
 
 } // namespace WebCore