Have Node::document() return a reference instead of a pointer

Source/core/html/HTMLParamElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Stefan Schimanski (1Stein@gmx.de)
  * Copyright (C) 2004, 2005, 2006, 2008, 2010 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 29 matching lines @@
 
 PassRefPtr<HTMLParamElement> HTMLParamElement::create(const QualifiedName& tagName, Document* document)
 {
     return adoptRef(new HTMLParamElement(tagName, document));
 }
 
 String HTMLParamElement::name() const
 {
     if (hasName())
         return getNameAttribute();
-    return document()->isHTMLDocument() ? emptyAtom : getIdAttribute();
+    return document().isHTMLDocument() ? emptyAtom : getIdAttribute();
 }
 
 String HTMLParamElement::value() const
 {
     return fastGetAttribute(valueAttr);
 }
 
 bool HTMLParamElement::isURLParameter(const String& name)
 {
     return equalIgnoringCase(name, "data") || equalIgnoringCase(name, "movie") || equalIgnoringCase(name, "src");
 }
 
 bool HTMLParamElement::isURLAttribute(const Attribute& attribute) const
 {
     if (attribute.name() == valueAttr && isURLParameter(name()))
         return true;
     return HTMLElement::isURLAttribute(attribute);
 }
 
 void HTMLParamElement::addSubresourceAttributeURLs(ListHashSet<KURL>& urls) const
 {
     HTMLElement::addSubresourceAttributeURLs(urls);
 
     if (!isURLParameter(name()))
         return;
 
-    addSubresourceURL(urls, document()->completeURL(value()));
+    addSubresourceURL(urls, document().completeURL(value()));
 }
 
 }