Use TreeScope::completeURL and baseURL instead of the Document versions

Source/core/html/HTMLVideoElement.cpp

 /*
  * Copyright (C) 2007, 2008, 2009, 2010 Apple 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 249 matching lines @@
         return 0;
 
     return player()->droppedFrameCount();
 }
 
 KURL HTMLVideoElement::posterImageURL() const
 {
     String url = stripLeadingAndTrailingHTMLSpaces(imageSourceURL());
     if (url.isEmpty())
         return KURL();
-    return document().completeURL(url);
+    return treeScope().completeURL(url);
 }
 
 }