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

chrome/browser/extensions/api/storage/policy_value_store.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_POLICY_VALUE_STORE_H_
 #define CHROME_BROWSER_EXTENSIONS_API_STORAGE_POLICY_VALUE_STORE_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 37 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;
+  // Hopefully, as a Read-Only database, there is no reason to use these.
+  virtual bool Restore() OVERRIDE;
+  virtual bool RestoreKey(const std::string& key) OVERRIDE;
 
   // For unit tests.
   ValueStore* delegate() { return delegate_.get(); }
 
  private:
   std::string extension_id_;
   scoped_refptr<SettingsObserverList> observers_;
   scoped_ptr<ValueStore> delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(PolicyValueStore);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_STORAGE_POLICY_VALUE_STORE_H_