Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/modules/mediastream/RTCStatsResponse.cpp

 /*
  * Copyright (C) 2012 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 24 matching lines @@
 
 RTCStatsResponse::RTCStatsResponse()
 {
     ScriptWrappable::init(this);
 }
 
 PassRefPtr<RTCStatsReport> RTCStatsResponse::namedItem(const AtomicString& name)
 {
     if (m_idmap.find(name) != m_idmap.end())
         return m_result[m_idmap.get(name)];
-    return 0;
+    return nullptr;
 }
 
 size_t RTCStatsResponse::addReport(String id, String type, double timestamp)
 {
     m_result.append(RTCStatsReport::create(id, type, timestamp));
     m_idmap.add(id, m_result.size() - 1);
     return m_result.size() - 1;
 }
 
 void RTCStatsResponse::addStatistic(size_t report, String name, String value)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(report >= 0 && report < m_result.size());
     m_result[report]->addStatistic(name, value);
 }
 
 } // namespace WebCore