Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/bindings/v8/V8ValueCache.cpp

 /*
  * Copyright (C) 2009 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 88 matching lines @@
     m_lastV8String = UnsafePersistent<v8::String>(wrapper);
     m_lastStringImpl = stringImpl;
     m_stringCache.set(stringImpl, m_lastV8String);
 
     return newString;
 }
 
 void StringCache::setWeakCallback(const v8::WeakCallbackData<v8::String, StringImpl>& data)
 {
     StringCache* stringCache = V8PerIsolateData::from(data.GetIsolate())->stringCache();
-    stringCache->m_lastStringImpl = 0;
+    stringCache->m_lastStringImpl = nullptr;
     stringCache->m_lastV8String.clear();
     ASSERT(stringCache->m_stringCache.contains(data.GetParameter()));
     stringCache->m_stringCache.get(data.GetParameter()).dispose();
     stringCache->m_stringCache.remove(data.GetParameter());
     data.GetParameter()->deref();
 }
 
 } // namespace WebCore