Use new Traversal<> API more in the code base

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 298 matching lines @@
     DEFINE_STATIC_LOCAL(WillBePersistentHeapVector<RefPtrWillBeMember<InsertionPoint> >, emptyList, ());
     if (m_shadowRootRareData && m_descendantInsertionPointsIsValid)
         return m_shadowRootRareData->descendantInsertionPoints();
 
     m_descendantInsertionPointsIsValid = true;
 
     if (!containsInsertionPoints())
         return emptyList;
 
     WillBeHeapVector<RefPtrWillBeMember<InsertionPoint> > insertionPoints;
-    for (Element* element = ElementTraversal::firstWithin(*this); element; element = ElementTraversal::next(*element, this)) {
-        if (element->isInsertionPoint())
-            insertionPoints.append(toInsertionPoint(element));
-    }
+    for (InsertionPoint* insertionPoint = Traversal<InsertionPoint>::firstWithin(*this); insertionPoint; insertionPoint = Traversal<InsertionPoint>::next(*insertionPoint, this))
+        insertionPoints.append(insertionPoint);
 
     ensureShadowRootRareData()->setDescendantInsertionPoints(insertionPoints);
 
     return m_shadowRootRareData->descendantInsertionPoints();
 }
 
 StyleSheetList* ShadowRoot::styleSheets()
 {
     if (!ensureShadowRootRareData()->styleSheets())
         m_shadowRootRareData->setStyleSheets(StyleSheetList::create(this));
 
     return m_shadowRootRareData->styleSheets();
 }
 
 void ShadowRoot::trace(Visitor* visitor)
 {
     visitor->trace(m_prev);
     visitor->trace(m_next);
     visitor->trace(m_shadowRootRareData);
     TreeScope::trace(visitor);
     DocumentFragment::trace(visitor);
 }
 
 }