extensions: Cleanup class/struct fwd declarations

extensions/shell/browser/shell_url_request_context_getter.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef EXTENSIONS_SHELL_BROWSER_SHELL_URL_REQUEST_CONTEXT_GETTER_H_
 #define EXTENSIONS_SHELL_BROWSER_SHELL_URL_REQUEST_CONTEXT_GETTER_H_
 
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "content/shell/browser/shell_url_request_context_getter.h"
 
-namespace base {
-class MessageLoop;
-}
-
 namespace content {
 class BrowserContext;
 }
 
 namespace net {
 class NetworkDelegate;
 class NetLog;
 }
 
 namespace extensions {
@@ skipping 24 matching lines @@
   content::BrowserContext* browser_context_;
   InfoMap* extension_info_map_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ShellURLRequestContextGetter);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_SHELL_BROWSER_SHELL_URL_REQUEST_CONTEXT_GETTER_H_