Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/dom/MutationObserverRegistration.cpp

 /*
  * Copyright (C) 2011 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 76 matching lines @@
         ASSERT(!m_registrationNodeKeepAlive);
         return;
     }
 
     for (NodeHashSet::iterator iter = m_transientRegistrationNodes->begin(); iter != m_transientRegistrationNodes->end(); ++iter)
         (*iter)->unregisterTransientMutationObserver(this);
 
     m_transientRegistrationNodes.clear();
 
     ASSERT(m_registrationNodeKeepAlive);
-    m_registrationNodeKeepAlive = 0; // Balanced in observeSubtreeNodeWillDetach.
+    m_registrationNodeKeepAlive = nullptr; // Balanced in observeSubtreeNodeWillDetach.
 }
 
 void MutationObserverRegistration::unregister()
 {
     m_registrationNode->unregisterMutationObserver(this);
     // The above line will cause this object to be deleted, so don't do any more in this function.
 }
 
 bool MutationObserverRegistration::shouldReceiveMutationFrom(Node* node, MutationObserver::MutationType type, const QualifiedName* attributeName) const
 {
@@ skipping 16 matching lines @@
 void MutationObserverRegistration::addRegistrationNodesToSet(HashSet<Node*>& nodes) const
 {
     nodes.add(m_registrationNode);
     if (!m_transientRegistrationNodes)
         return;
     for (NodeHashSet::const_iterator iter = m_transientRegistrationNodes->begin(); iter != m_transientRegistrationNodes->end(); ++iter)
         nodes.add(iter->get());
 }
 
 } // namespace WebCore