Clean up forward declarations in Source/core/fetch and /loader

Source/core/loader/FrameLoaderClient.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 43 matching lines @@
 
     class DocumentLoader;
     class FetchRequest;
     class HTMLAppletElement;
     class HTMLFormElement;
     class HTMLFrameOwnerElement;
     class HTMLPlugInElement;
     class HistoryItem;
     class KURL;
     class LocalFrame;
-    class MessageEvent;
     class ResourceError;
     class ResourceRequest;
     class ResourceResponse;
     class SecurityOrigin;
     class SharedWorkerRepositoryClient;
     class SocketStreamHandle;
     class SubstituteData;
     class Widget;
 
     class FrameLoaderClient : public FrameClient {
@@ skipping 141 matching lines @@
         virtual void didStopAllLoaders() { }
 
         virtual void dispatchDidChangeManifest() { }
 
         virtual bool isFrameLoaderClientImpl() const { return false; }
     };
 
 } // namespace blink
 
 #endif // FrameLoaderClient_h