Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/dom/ElementDataCache.cpp

 /*
  * Copyright (C) 2012, 2013 Apple 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 29 matching lines @@
 {
     if (attributes.size() != elementData.length())
         return false;
     return !memcmp(attributes.data(), elementData.m_attributeArray, attributes.size() * sizeof(Attribute));
 }
 
 PassRefPtr<ShareableElementData> ElementDataCache::cachedShareableElementDataWithAttributes(const Vector<Attribute>& attributes)
 {
     ASSERT(!attributes.isEmpty());
 
-    ShareableElementDataCache::ValueType* it = m_shareableElementDataCache.add(attributeHash(attributes), 0).storedValue;
+    ShareableElementDataCache::ValueType* it = m_shareableElementDataCache.add(attributeHash(attributes), nullptr).storedValue;
 
     // FIXME: This prevents sharing when there's a hash collision.
     if (it->value && !hasSameAttributes(attributes, *it->value))
         return ShareableElementData::createWithAttributes(attributes);
 
     if (!it->value)
         it->value = ShareableElementData::createWithAttributes(attributes);
 
     return it->value.get();
 }
 
 ElementDataCache::ElementDataCache()
 {
 }
 
 ElementDataCache::~ElementDataCache()
 {
 }
 
 }