[Sync] Adding storage key concept for ModelTypeServices.

components/sync/api/metadata_change_list.h

Index: components/sync/api/metadata_change_list.h
diff --git a/components/sync/api/metadata_change_list.h b/components/sync/api/metadata_change_list.h
index 13d329998b9e30ab8238ae1e6660fce26aa60df6..5ab9ba63cd253fb922dcb00e06fe67f2743037bc 100644
--- a/components/sync/api/metadata_change_list.h
+++ b/components/sync/api/metadata_change_list.h
@@ -40,11 +40,11 @@ class SYNC_EXPORT MetadataChangeList {
   // 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