extensions: Cleanup class/struct fwd declarations

extensions/common/extension_api.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_COMMON_EXTENSION_API_H_
 #define EXTENSIONS_COMMON_EXTENSION_API_H_
 
 #include <map>
 #include <memory>
 #include <string>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/singleton.h"
 #include "base/strings/string_piece.h"
 #include "base/values.h"
 #include "extensions/common/features/feature.h"
 #include "extensions/common/features/feature_provider.h"
 #include "extensions/common/url_pattern_set.h"
 
 namespace base {
 class DictionaryValue;
-class Value;
 }
 
 class GURL;
 
 namespace extensions {
 
 class Extension;
 class ExtensionsClient;
 class Feature;
 
@@ skipping 118 matching lines @@
   // FeatureProviders used for resolving dependencies.
   typedef std::map<std::string, const FeatureProvider*> FeatureProviderMap;
   FeatureProviderMap dependency_providers_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionAPI);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_COMMON_EXTENSION_API_H_