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

chrome/browser/extensions/api/storage/leveldb_settings_storage_factory.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_LEVELDB_SETTINGS_STORAGE_FACTORY_H_
 #define CHROME_BROWSER_EXTENSIONS_API_STORAGE_LEVELDB_SETTINGS_STORAGE_FACTORY_H_
 
 #include "chrome/browser/extensions/api/storage/settings_storage_factory.h"
 
 namespace extensions {
 
 // Factory for creating LeveldbValueStore instances.
 class LeveldbSettingsStorageFactory : public SettingsStorageFactory {
  public:
   virtual ValueStore* Create(const base::FilePath& base_path,
                              const std::string& extension_id) OVERRIDE;
 
+  virtual void DeleteDatabaseIfExists(const base::FilePath& base_path,
+                                      const std::string& extension_id) OVERRIDE;
+
  private:
   // SettingsStorageFactory is refcounted.
   virtual ~LeveldbSettingsStorageFactory() {}
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_STORAGE_LEVELDB_SETTINGS_STORAGE_FACTORY_H_