Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/events/MutationEvent.h

 /*
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2001 Tobias Anton (anton@stud.fbi.fh-darmstadt.de)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2008 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 26 matching lines @@
             MODIFICATION    = 1,
             ADDITION        = 2,
             REMOVAL         = 3
         };
 
         static PassRefPtr<MutationEvent> create()
         {
             return adoptRef(new MutationEvent);
         }
 
-        static PassRefPtr<MutationEvent> create(const AtomicString& type, bool canBubble, PassRefPtr<Node> relatedNode = 0,
+        static PassRefPtr<MutationEvent> create(const AtomicString& type, bool canBubble, PassRefPtr<Node> relatedNode = nullptr,
             const String& prevValue = String(), const String& newValue = String(), const String& attrName = String(), unsigned short attrChange = 0)
         {
             return adoptRef(new MutationEvent(type, canBubble, false, relatedNode, prevValue, newValue, attrName, attrChange));
         }
 
         void initMutationEvent(const AtomicString& type, bool canBubble, bool cancelable, PassRefPtr<Node> relatedNode,
                                const String& prevValue, const String& newValue,
                                const String& attrName, unsigned short attrChange);
 
         Node* relatedNode() const { return m_relatedNode.get(); }
@@ skipping 13 matching lines @@
         RefPtr<Node> m_relatedNode;
         String m_prevValue;
         String m_newValue;
         String m_attrName;
         unsigned short m_attrChange;
     };
 
 } // namespace WebCore
 
 #endif // MutationEvent_h