[Sync] Adding a passthrough MetadataChangeList implementation.

components/sync/model/simple_metadata_change_list.cc

 // 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.
 
 #include "components/sync/model/simple_metadata_change_list.h"
 
 namespace syncer {
 
 SimpleMetadataChangeList::SimpleMetadataChangeList() {}
 
 SimpleMetadataChangeList::~SimpleMetadataChangeList() {}
 
 void SimpleMetadataChangeList::UpdateModelTypeState(
     const sync_pb::ModelTypeState& model_type_state) {
   state_change_.reset(new ModelTypeStateChange{UPDATE, model_type_state});
 }
 
 void SimpleMetadataChangeList::ClearModelTypeState() {
   state_change_.reset(new ModelTypeStateChange{CLEAR});
 }
 
 void SimpleMetadataChangeList::UpdateMetadata(
-    const std::string& client_tag,
+    const std::string& storage_key,
     const sync_pb::EntityMetadata& metadata) {
-  metadata_changes_[client_tag] = {UPDATE, metadata};
+  metadata_changes_[storage_key] = {UPDATE, metadata};
 }
 
-void SimpleMetadataChangeList::ClearMetadata(const std::string& client_tag) {
-  metadata_changes_[client_tag] = {CLEAR, sync_pb::EntityMetadata()};
+void SimpleMetadataChangeList::ClearMetadata(const std::string& storage_key) {
+  metadata_changes_[storage_key] = {CLEAR, sync_pb::EntityMetadata()};
 }
 
 const SimpleMetadataChangeList::MetadataChanges&
 SimpleMetadataChangeList::GetMetadataChanges() const {
   return metadata_changes_;
 }
 
 bool SimpleMetadataChangeList::HasModelTypeStateChange() const {
   return state_change_.get() != nullptr;
 }
 
 const SimpleMetadataChangeList::ModelTypeStateChange&
 SimpleMetadataChangeList::GetModelTypeStateChange() const {
   return *state_change_.get();
 }
 
 void SimpleMetadataChangeList::TransferChanges(
     ModelTypeStore* store,
     ModelTypeStore::WriteBatch* write_batch) {
   DCHECK(write_batch);
   DCHECK(store);
   for (const auto& pair : metadata_changes_) {
-    const std::string& key = pair.first;
+    const std::string& storage_key = pair.first;
     const MetadataChange& change = pair.second;
     switch (change.type) {
       case UPDATE:
-        store->WriteMetadata(write_batch, key,
+        store->WriteMetadata(write_batch, storage_key,
                              change.metadata.SerializeAsString());
         break;
       case CLEAR:
-        store->DeleteMetadata(write_batch, key);
+        store->DeleteMetadata(write_batch, storage_key);
         break;
     }
   }
   metadata_changes_.clear();
   if (HasModelTypeStateChange()) {
     switch (state_change_->type) {
       case UPDATE:
         store->WriteGlobalMetadata(write_batch,
                                    state_change_->state.SerializeAsString());
         break;
       case CLEAR:
         store->DeleteGlobalMetadata(write_batch);
         break;
     }
     state_change_.reset();
   }
 }
 
 }  // namespace syncer