[Sync] Adding a passthrough MetadataChangeList implementation.

components/sync/model/simple_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_MODEL_SIMPLE_METADATA_CHANGE_LIST_H_
 #define COMPONENTS_SYNC_MODEL_SIMPLE_METADATA_CHANGE_LIST_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 24 matching lines @@
   };
 
   typedef std::map<std::string, MetadataChange> MetadataChanges;
 
   SimpleMetadataChangeList();
   ~SimpleMetadataChangeList() override;
 
   void UpdateModelTypeState(
       const sync_pb::ModelTypeState& model_type_state) override;
   void ClearModelTypeState() override;
-  void UpdateMetadata(const std::string& client_tag,
+  void UpdateMetadata(const std::string& storage_key,
                       const sync_pb::EntityMetadata& metadata) override;
-  void ClearMetadata(const std::string& client_tag) override;
+  void ClearMetadata(const std::string& storage_key) override;
 
   const MetadataChanges& GetMetadataChanges() const;
   bool HasModelTypeStateChange() const;
   const ModelTypeStateChange& GetModelTypeStateChange() const;
 
   // Moves all currently accumulated changes into the write batch, clear out
   // local copies. Calling this multiple times will work, but should not be
   // necessary.
   void TransferChanges(ModelTypeStore* store,
                        ModelTypeStore::WriteBatch* write_batch);
 
  private:
   MetadataChanges metadata_changes_;
   std::unique_ptr<ModelTypeStateChange> state_change_;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_MODEL_SIMPLE_METADATA_CHANGE_LIST_H_