Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/xml/DOMParser.cpp

 /*
  *  Copyright (C) 2003, 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 Lesser 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,
  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 19 matching lines @@
 PassRefPtr<Document> DOMParser::parseFromString(const String& str, const String& contentType, ExceptionState& exceptionState)
 {
     // HTML5 is very explicit about which types we're allowed to support here:
     // http://domparsing.spec.whatwg.org/#the-domparser-interface
     if (contentType != "text/html"
         && contentType != "text/xml"
         && contentType != "application/xml"
         && contentType != "application/xhtml+xml"
         && contentType != "image/svg+xml") {
         exceptionState.throwDOMException(TypeError, "Unsupported mime-type specified.");
-        return 0;
+        return nullptr;
     }
 
     RefPtr<Document> doc = DOMImplementation::createDocument(contentType, 0, KURL(), false);
     doc->setContent(str);
     return doc.release();
 }
 
 } // namespace WebCore