Use nullptr_t for RefPtr, PassRefPtr and RawPtr.

Source/core/xml/XSLTProcessorLibxslt.cpp

 /*
  * This file is part of the XSL implementation.
  *
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple, Inc. All rights reserved.
  * Copyright (C) 2005, 2006 Alexey Proskuryakov <ap@webkit.org>
  *
  * 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 262 matching lines @@
 }
 
 bool XSLTProcessor::transformToString(Node* sourceNode, String& mimeType, String& resultString, String& resultEncoding)
 {
     RefPtr<Document> ownerDocument(sourceNode->document());
 
     setXSLTLoadCallBack(docLoaderFunc, this, ownerDocument->fetcher());
     xsltStylesheetPtr sheet = xsltStylesheetPointer(m_stylesheet, m_stylesheetRootNode.get());
     if (!sheet) {
         setXSLTLoadCallBack(0, 0, 0);
-        m_stylesheet = 0;
+        m_stylesheet = nullptr;
         return false;
     }
     m_stylesheet->clearDocuments();
 
     xmlChar* origMethod = sheet->method;
     if (!origMethod && mimeType == "text/html")
         sheet->method = (xmlChar*)"html";
 
     bool success = false;
     bool shouldFreeSourceDoc = false;
@@ skipping 38 matching lines @@
         if ((success = saveResultToString(resultDoc, sheet, resultString))) {
             mimeType = resultMIMEType(resultDoc, sheet);
             resultEncoding = (char*)resultDoc->encoding;
         }
         xmlFreeDoc(resultDoc);
     }
 
     sheet->method = origMethod;
     setXSLTLoadCallBack(0, 0, 0);
     xsltFreeStylesheet(sheet);
-    m_stylesheet = 0;
+    m_stylesheet = nullptr;
 
     return success;
 }
 
 } // namespace WebCore