[Sync] Support commit only types.

components/sync/user_events/user_event_sync_bridge.cc

Index: components/sync/user_events/user_event_sync_bridge.cc
diff --git a/components/sync/user_events/user_event_sync_bridge.cc b/components/sync/user_events/user_event_sync_bridge.cc
index 51e058ad5bd374c12cbd831b29963a3eb1d3b1bf..f601791b85c593b3c855c669e410b7b26746c723 100644
--- a/components/sync/user_events/user_event_sync_bridge.cc
+++ b/components/sync/user_events/user_event_sync_bridge.cc
@@ -84,7 +84,15 @@ base::Optional<ModelError> UserEventSyncBridge::MergeSyncData(
 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 {};
 }