[Sync] Improve MetadataChangeList usage for types using ModelTypeStore.

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& storage_key,
-    const sync_pb::EntityMetadata& metadata) {
-  metadata_changes_[storage_key] = {UPDATE, metadata};
-}
-
-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& storage_key = pair.first;
-    const MetadataChange& change = pair.second;
-    switch (change.type) {
-      case UPDATE:
-        store->WriteMetadata(write_batch, storage_key,
-                             change.metadata.SerializeAsString());
-        break;
-      case CLEAR:
-        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