Clean up forward declarations in Source/core/events

Source/core/xml/XMLHttpRequest.h

 /*
  *  Copyright (C) 2003, 2006, 2008 Apple Inc. All rights reserved.
  *  Copyright (C) 2005, 2006 Alexey Proskuryakov <ap@nypop.com>
  *  Copyright (C) 2011 Google Inc. All rights reserved.
  *  Copyright (C) 2012 Intel Corporation
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
  *  version 2 of the License, or (at your option) any later version.
@@ skipping 35 matching lines @@
 class Document;
 class DocumentParser;
 class ExceptionState;
 class ResourceRequest;
 class SecurityOrigin;
 class SharedBuffer;
 class Stream;
 class TextResourceDecoder;
 class ThreadableLoader;
 class UnderlyingSource;
+class XMLHttpRequestUpload;
 
 typedef int ExceptionCode;
 
 class XMLHttpRequest final
     : public RefCountedWillBeGarbageCollectedFinalized<XMLHttpRequest>
     , public XMLHttpRequestEventTarget
     , private ThreadableLoaderClient
     , public DocumentParserClient
     , public ActiveDOMObject {
     DEFINE_WRAPPERTYPEINFO();
@@ skipping 239 matching lines @@
     bool m_uploadComplete;
     bool m_sameOriginRequest;
     // True iff the ongoing resource loading is using the downloadToFile
     // option.
     bool m_downloadingToFile;
 };
 
 } // namespace blink
 
 #endif // XMLHttpRequest_h