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

Source/web/WebPageSerializer.cpp

 /*
  * Copyright (C) 2009 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 82 matching lines @@
         attributeName = &HTMLNames::srcAttr;
 
     if (!attributeName)
         return KURL();
 
     String value = element->getAttribute(*attributeName);
     // Ignore javascript content.
     if (value.isEmpty() || value.stripWhiteSpace().startsWith("javascript:", false))
         return KURL();
 
-    return element->document()->completeURL(value);
+    return element->document().completeURL(value);
 }
 
 void retrieveResourcesForElement(Element* element,
                                  Vector<Frame*>* visitedFrames,
                                  Vector<Frame*>* framesToVisit,
                                  Vector<KURL>* frameURLs,
                                  Vector<KURL>* resourceURLs)
 {
     // If the node is a frame, we'll process it later in retrieveResourcesForFrame.
     if ((element->hasTagName(HTMLNames::iframeTag) || element->hasTagName(HTMLNames::frameTag)
@@ skipping 178 matching lines @@
 
 WebString WebPageSerializer::generateBaseTagDeclaration(const WebString& baseTarget)
 {
     if (baseTarget.isEmpty())
         return String("<base href=\".\">");
     String baseString = "<base href=\".\" target=\"" + static_cast<const String&>(baseTarget) + "\">";
     return baseString;
 }
 
 } // namespace WebKit