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

Source/core/html/HTMLTrackElement.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.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 100 matching lines @@
             track()->setLanguage(value);
         else if (name == defaultAttr)
             track()->setIsDefault(!value.isNull());
     }
 
     HTMLElement::parseAttribute(name, value);
 }
 
 KURL HTMLTrackElement::src() const
 {
-    return document()->completeURL(getAttribute(srcAttr));
+    return document().completeURL(getAttribute(srcAttr));
 }
 
 void HTMLTrackElement::setSrc(const String& url)
 {
     setAttribute(srcAttr, url);
 }
 
 String HTMLTrackElement::kind()
 {
     return track()->kind();
@@ skipping 113 matching lines @@
         return false;
 
     // 4.8.10.12.3 Sourcing out-of-band text tracks
 
     // 4. Download: If URL is not the empty string, perform a potentially CORS-enabled fetch of URL, with the
     // mode being the state of the media element's crossorigin content attribute, the origin being the
     // origin of the media element's Document, and the default origin behaviour set to fail.
     if (url.isEmpty())
         return false;
 
-    if (!document()->contentSecurityPolicy()->allowMediaFromSource(url)) {
+    if (!document().contentSecurityPolicy()->allowMediaFromSource(url)) {
         LOG(Media, "HTMLTrackElement::canLoadUrl(%s) -> rejected by Content Security Policy", urlForLoggingTrack(url).utf8().data());
         return false;
     }
 
     return dispatchBeforeLoadEvent(url.string());
 }
 
 void HTMLTrackElement::didCompleteLoad(LoadableTextTrack*, LoadStatus status)
 {
     // 4.8.10.12.3 Sourcing out-of-band text tracks (continued)
@@ skipping 91 matching lines @@
 HTMLMediaElement* HTMLTrackElement::mediaElement() const
 {
     Element* parent = parentElement();
     if (parent && parent->isMediaElement())
         return toHTMLMediaElement(parentNode());
     return 0;
 }
 
 }