Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/dom/ContainerNode.h

 /*
  * 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, 2009, 2010, 2011 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 281 matching lines @@
     PassRefPtr<Node> nextNode()
     {
         if (LIKELY(!hasSnapshot())) {
             RefPtr<Node> node = m_currentNode;
             if (node)
                 m_currentNode = node->nextSibling();
             return node.release();
         }
         Vector<RefPtr<Node> >& nodeVector = *m_childNodes;
         if (m_currentIndex >= nodeVector.size())
-            return 0;
+            return nullptr;
         return nodeVector[m_currentIndex++];
     }
 
     void takeSnapshot()
     {
         if (hasSnapshot())
             return;
         m_childNodes = adoptPtr(new Vector<RefPtr<Node> >());
         Node* node = m_currentNode.get();
         while (node) {
@@ skipping 19 matching lines @@
 
     RefPtr<Node> m_currentNode;
     unsigned m_currentIndex;
     OwnPtr<Vector<RefPtr<Node> > > m_childNodes; // Lazily instantiated.
     ChildNodesLazySnapshot* m_nextSnapshot;
 };
 
 } // namespace WebCore
 
 #endif // ContainerNode_h