Add a Restore() method to ValueStore and make StorageAPI use it

chrome/browser/extensions/api/storage/syncable_settings_storage.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_SYNCABLE_SETTINGS_STORAGE_H_
 #define CHROME_BROWSER_EXTENSIONS_API_STORAGE_SYNCABLE_SETTINGS_STORAGE_H_
 
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 31 matching lines @@
   virtual ReadResult Get() OVERRIDE;
   virtual WriteResult Set(
       WriteOptions options,
       const std::string& key,
       const base::Value& value) OVERRIDE;
   virtual WriteResult Set(
       WriteOptions options, const base::DictionaryValue& values) OVERRIDE;
   virtual WriteResult Remove(const std::string& key) OVERRIDE;
   virtual WriteResult Remove(const std::vector<std::string>& keys) OVERRIDE;
   virtual WriteResult Clear() OVERRIDE;
+  virtual bool Restore() OVERRIDE;
+  virtual bool RestoreKey(const std::string& key) OVERRIDE;
 
   // Sync-related methods, analogous to those on SyncableService (handled by
   // ExtensionSettings), but with looser guarantees about when the methods
   // can be called.
 
   // Must only be called if sync isn't already active.
   syncer::SyncError StartSyncing(
       const base::DictionaryValue& sync_state,
       scoped_ptr<SettingsSyncProcessor> sync_processor);
 
@@ skipping 46 matching lines @@
 
   const syncer::ModelType sync_type_;
   const syncer::SyncableService::StartSyncFlare flare_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncableSettingsStorage);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_STORAGE_SYNCABLE_SETTINGS_STORAGE_H_