Use more references in ContainerNode code

Source/core/xml/XMLErrors.cpp

 /*
  * Copyright (C) 2011 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.
  *
@@ skipping 133 matching lines @@
         Vector<Attribute> attributes;
         attributes.append(Attribute(styleAttr, "white-space: normal"));
         RefPtr<Element> paragraph = m_document->createElement(pTag, true);
         paragraph->parserSetAttributes(attributes);
         paragraph->parserAppendChild(m_document->createTextNode("This document was created as the result of an XSL transformation. The line and column numbers given are from the transformed result."));
         reportElement->parserAppendChild(paragraph.release());
     }
 
     Node* firstChild = documentElement->firstChild();
     if (firstChild)
-        documentElement->parserInsertBefore(reportElement, documentElement->firstChild());
+        documentElement->parserInsertBefore(reportElement, *firstChild);
     else
         documentElement->parserAppendChild(reportElement);
 
     // FIXME: Why do we need to call this manually?
     m_document->updateStyleIfNeeded();
 }
 
 } // namespace WebCore