Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/css/Pair.h

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 49 matching lines @@
     {
         return compareCSSValuePtr(m_first, other.m_first)
             && compareCSSValuePtr(m_second, other.m_second)
             && m_identicalValuesPolicy == other.m_identicalValuesPolicy;
     }
 
     void trace(Visitor*);
 
 private:
     Pair()
-        : m_first(0)
-        , m_second(0)
+        : m_first(nullptr)
+        , m_second(nullptr)
         , m_identicalValuesPolicy(DropIdenticalValues) { }
 
     Pair(PassRefPtrWillBeRawPtr<CSSPrimitiveValue> first, PassRefPtrWillBeRawPtr<CSSPrimitiveValue> second, IdenticalValuesPolicy identicalValuesPolicy)
         : m_first(first)
         , m_second(second)
         , m_identicalValuesPolicy(identicalValuesPolicy) { }
 
     static String generateCSSString(const String& first, const String& second, IdenticalValuesPolicy identicalValuesPolicy)
     {
         if (identicalValuesPolicy == DropIdenticalValues && first == second)
             return first;
         return first + ' ' + second;
     }
 
     RefPtrWillBeMember<CSSPrimitiveValue> m_first;
     RefPtrWillBeMember<CSSPrimitiveValue> m_second;
     IdenticalValuesPolicy m_identicalValuesPolicy;
 };
 
 } // namespace
 
 #endif