Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/platform/PODRedBlackTree.h

 /*
  * Copyright (C) 2010 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 132 matching lines @@
     {
     }
 
     virtual ~PODRedBlackTree() { }
 
     // Clearing will delete the contents of the tree. After this call
     // isInitialized will return false.
     void clear()
     {
         markFree(m_root);
-        m_arena = 0;
+        m_arena = nullptr;
         m_root = 0;
     }
 
     bool isInitialized() const
     {
         return m_arena;
     }
 
     void initIfNeeded()
     {
@@ skipping 655 matching lines @@
     Node* m_root;
     bool m_needsFullOrderingComparisons;
 #ifndef NDEBUG
     bool m_verboseDebugging;
 #endif
 };
 
 } // namespace WebCore
 
 #endif // PODRedBlackTree_h