[Sync] Adding storage key concept for ModelTypeServices.

components/sync/api/metadata_change_list.h

 // Copyright 2015 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 COMPONENTS_SYNC_API_METADATA_CHANGE_LIST_H_
 #define COMPONENTS_SYNC_API_METADATA_CHANGE_LIST_H_
 
 #include <string>
 
 #include "components/sync/base/sync_export.h"
@@ skipping 22 matching lines @@
   virtual void UpdateDataTypeState(
       const sync_pb::DataTypeState& data_type_state) = 0;
 
   // Requests DataTypeState to be cleared from the storage.
   virtual void ClearDataTypeState() = 0;
 
   // Requests metadata entry to be updated in the storage.
   // Please note that the update might contain a deleted entry if
   // metadata.is_deleted() is true (as opposed to clearing the entry from the
   // storage completely by calling the Clear method).
-  virtual void UpdateMetadata(const std::string& client_tag,
+  virtual void UpdateMetadata(const std::string& storage_key,
                               const sync_pb::EntityMetadata& metadata) = 0;
 
   // Requests metadata entry to be cleared from the storage.
-  virtual void ClearMetadata(const std::string& client_tag) = 0;
+  virtual void ClearMetadata(const std::string& storage_key) = 0;
 };
 
 }  // namespace syncer_v2
 
 #endif  // COMPONENTS_SYNC_API_METADATA_CHANGE_LIST_H_