extensions: Cleanup class/struct fwd declarations

extensions/renderer/script_context_set.h

 // Copyright 2014 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_RENDERER_SCRIPT_CONTEXT_SET_H_
 #define EXTENSIONS_RENDERER_SCRIPT_CONTEXT_SET_H_
 
 #include <stddef.h>
 
 #include <set>
 #include <string>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/features/feature.h"
 #include "extensions/renderer/renderer_extension_registry.h"
 #include "url/gurl.h"
 #include "v8/include/v8.h"
 
 class GURL;
 
-namespace base {
-class ListValue;
-}
-
 namespace blink {
 class WebLocalFrame;
 class WebSecurityOrigin;
 }
 
 namespace content {
 class RenderFrame;
 }
 
 namespace extensions {
@@ skipping 102 matching lines @@
 
   // The set of all ScriptContexts we own.
   std::set<ScriptContext*> contexts_;
 
   DISALLOW_COPY_AND_ASSIGN(ScriptContextSet);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_RENDERER_SCRIPT_CONTEXT_SET_H_