Add ExtensionsApiClient interface, use it in the storage API SettingsFrontend

chrome/browser/extensions/api/storage/settings_frontend.h

 // Copyright (c) 2012 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 CHROME_BROWSER_EXTENSIONS_API_STORAGE_SETTINGS_FRONTEND_H_
 #define CHROME_BROWSER_EXTENSIONS_API_STORAGE_SETTINGS_FRONTEND_H_
 
 #include <map>
 #include <string>
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "chrome/browser/extensions/api/profile_keyed_api_factory.h"
-#include "chrome/browser/extensions/api/storage/settings_namespace.h"
 #include "chrome/browser/extensions/api/storage/settings_observer.h"
 #include "chrome/browser/extensions/api/storage/settings_storage_factory.h"
 #include "chrome/browser/extensions/api/storage/settings_storage_quota_enforcer.h"
 #include "chrome/browser/extensions/api/storage/value_store_cache.h"
+#include "extensions/browser/api/storage/settings_namespace.h"
 #include "sync/api/syncable_service.h"
 
 namespace content {
 class BrowserContext;
 }
 
 namespace extensions {
 
 // The component of extension settings which runs on the UI thread, as opposed
 // to SettingsBackend which lives on the FILE thread.
@@ skipping 71 matching lines @@
   // Maps a known namespace to its corresponding ValueStoreCache. The caches
   // are owned by this object.
   CacheMap caches_;
 
   DISALLOW_COPY_AND_ASSIGN(SettingsFrontend);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_STORAGE_SETTINGS_FRONTEND_H_