Use nullptr instead of 0 in xml and xmlhttprequest.

Source/core/xml/XSLImportRule.cpp

 /*
  * This file is part of the XSL implementation.
  *
  * Copyright (C) 2004, 2005, 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 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 54 matching lines @@
         parent->checkLoaded();
 }
 
 bool XSLImportRule::isLoading()
 {
     return m_loading || (m_styleSheet && m_styleSheet->isLoading());
 }
 
 void XSLImportRule::loadSheet()
 {
-    Document* ownerDocument = 0;
+    Document* ownerDocument = nullptr;
     XSLStyleSheet* rootSheet = parentStyleSheet();
 
     if (rootSheet) {
         while (XSLStyleSheet* parentSheet = rootSheet->parentStyleSheet())
             rootSheet = parentSheet;
     }
 
     if (rootSheet)
         ownerDocument = rootSheet->ownerDocument();
 
@@ skipping 23 matching lines @@
         setXSLStyleSheet(absHref, resource->response().url(), UTF8Encoding().decode(data->data(), data->size()));
 }
 
 DEFINE_TRACE(XSLImportRule)
 {
     visitor->trace(m_parentStyleSheet);
     visitor->trace(m_styleSheet);
 }
 
 } // namespace blink