Update fetch / loader classes to use OVERRIDE / FINAL when needed

Source/web/AssociatedURLLoader.cpp

 /*
  * Copyright (C) 2010, 2011, 2012 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 122 matching lines @@
     virtual void willSendRequest(ResourceRequest& /*newRequest*/, const ResourceResponse& /*redirectResponse*/);
 
     virtual void didReceiveResponse(unsigned long, const ResourceResponse&);
     virtual void didDownloadData(int /*dataLength*/);
     virtual void didReceiveData(const char*, int /*dataLength*/);
     virtual void didReceiveCachedMetadata(const char*, int /*dataLength*/);
     virtual void didFinishLoading(unsigned long /*identifier*/, double /*finishTime*/);
     virtual void didFail(const ResourceError&);
     virtual void didFailRedirectCheck();
 
-    virtual bool isDocumentThreadableLoaderClient() { return true; }
-
     // Sets an error to be reported back to the client, asychronously.
     void setDelayedError(const ResourceError&);
 
     // Enables forwarding of error notifications to the WebURLLoaderClient. These must be
     // deferred until after the call to AssociatedURLLoader::loadAsynchronously() completes.
     void enableErrorNotifications();
 
     // Stops loading and releases the DocumentThreadableLoader as early as possible.
     void clearClient() { m_client = 0; }
 
@@ skipping 212 matching lines @@
         m_loader->cancel();
 }
 
 void AssociatedURLLoader::setDefersLoading(bool defersLoading)
 {
     if (m_loader)
         m_loader->setDefersLoading(defersLoading);
 }
 
 } // namespace blink