Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/modules/mediastream/RTCSessionDescription.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
@@ skipping 36 matching lines @@
 {
     return "Illegal value of attribute 'type' : " + type;
 }
 
 PassRefPtr<RTCSessionDescription> RTCSessionDescription::create(const Dictionary& descriptionInitDict, ExceptionState& exceptionState)
 {
     String type;
     bool ok = descriptionInitDict.get("type", type);
     if (ok && !verifyType(type)) {
         exceptionState.throwDOMException(TypeMismatchError, constructIllegalTypeExceptionMessage(type));
-        return 0;
+        return nullptr;
     }
 
     String sdp;
     descriptionInitDict.get("sdp", sdp);
 
     return adoptRef(new RTCSessionDescription(blink::WebRTCSessionDescription(type, sdp)));
 }
 
 PassRefPtr<RTCSessionDescription> RTCSessionDescription::create(blink::WebRTCSessionDescription webSessionDescription)
 {
@@ skipping 28 matching lines @@
 {
     m_webSessionDescription.setSDP(sdp);
 }
 
 blink::WebRTCSessionDescription RTCSessionDescription::webSessionDescription()
 {
     return m_webSessionDescription;
 }
 
 } // namespace WebCore