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

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

Index: chrome/browser/extensions/api/storage/syncable_settings_storage.h
diff --git a/chrome/browser/extensions/api/storage/syncable_settings_storage.h b/chrome/browser/extensions/api/storage/syncable_settings_storage.h
index 3c04f3b45460b5ad64960c64c616c260916a56e9..5477066c8d4fb812e8f3a596cfea885bee8526b4 100644
--- a/chrome/browser/extensions/api/storage/syncable_settings_storage.h
+++ b/chrome/browser/extensions/api/storage/syncable_settings_storage.h
@@ -49,6 +49,8 @@ class SyncableSettingsStorage : public ValueStore {
   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