[Sync] Support commit only types.

components/sync/user_events/user_event_sync_bridge.cc

 // Copyright 2017 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/user_events/user_event_sync_bridge.h"
 
 #include <utility>
 
 #include "base/big_endian.h"
 #include "base/bind.h"
@@ skipping 66 matching lines @@
 base::Optional<ModelError> UserEventSyncBridge::MergeSyncData(
     std::unique_ptr<MetadataChangeList> metadata_change_list,
     EntityDataMap entity_data_map) {
   NOTREACHED();
   return {};
 }
 
 base::Optional<ModelError> UserEventSyncBridge::ApplySyncChanges(
     std::unique_ptr<MetadataChangeList> metadata_change_list,
     EntityChangeList entity_changes) {
-  NOTREACHED();
+  std::unique_ptr<WriteBatch> batch = store_->CreateWriteBatch();
+  for (EntityChange& change : entity_changes) {
+    DCHECK_EQ(EntityChange::ACTION_DELETE, change.type());
+    batch->DeleteData(change.storage_key());
+  }
+  batch->TransferMetadataChanges(std::move(metadata_change_list));
+  store_->CommitWriteBatch(
+      std::move(batch),
+      base::Bind(&UserEventSyncBridge::OnCommit, base::AsWeakPtr(this)));
   return {};
 }
 
 void UserEventSyncBridge::GetData(StorageKeyList storage_keys,
                                   DataCallback callback) {
   store_->ReadData(storage_keys, base::Bind(&UserEventSyncBridge::OnReadData,
                                             base::AsWeakPtr(this), callback));
 }
 
 void UserEventSyncBridge::GetAllData(DataCallback callback) {
@@ skipping 107 matching lines @@
   std::unique_ptr<WriteBatch> batch = store_->CreateWriteBatch();
   for (const Record& r : *data_records) {
     batch->DeleteData(r.id);
   }
   store_->CommitWriteBatch(
       std::move(batch),
       base::Bind(&UserEventSyncBridge::OnCommit, base::AsWeakPtr(this)));
 }
 
 }  // namespace syncer