extensions: Cleanup class/struct fwd declarations

extensions/browser/value_store/value_store_frontend.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_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_
 #define EXTENSIONS_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_
 
 #include <memory>
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/values.h"
 #include "extensions/browser/value_store/value_store.h"
 
-namespace base {
-class FilePath;
-}
-
 namespace extensions {
 class ValueStoreFactory;
 }  // namespace extensions
 
 // A frontend for a LeveldbValueStore, for use on the UI thread.
 class ValueStoreFrontend
     : public base::SupportsWeakPtr<ValueStoreFrontend>,
       public base::NonThreadSafe {
  public:
   // The kind of extensions data stored in a backend.
@@ skipping 20 matching lines @@
   class Backend;
 
   // A helper class to manage lifetime of the backing ValueStore, which lives
   // on the FILE thread.
   scoped_refptr<Backend> backend_;
 
   DISALLOW_COPY_AND_ASSIGN(ValueStoreFrontend);
 };
 
 #endif  // EXTENSIONS_BROWSER_VALUE_STORE_VALUE_STORE_FRONTEND_H_