[Sync] Add ModelTypeStore implementation.

sync/internal_api/model_type_store_backend.cc

Index: sync/internal_api/model_type_store_backend.cc
diff --git a/sync/internal_api/model_type_store_backend.cc b/sync/internal_api/model_type_store_backend.cc
new file mode 100644
index 0000000000000000000000000000000000000000..dc4cf1f694739604c4c79e2f390e53588dbb2a52
--- /dev/null
+++ b/sync/internal_api/model_type_store_backend.cc
@@ -0,0 +1,24 @@
+// 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 "sync/internal_api/public/model_type_store_backend.h"
+
+namespace syncer_v2 {
+
+ModelTypeStoreBackend::ModelTypeStoreBackend() {
+  // ModelTypeStoreBackend is used on different thread from the one where it is
+  // created.
+  DetachFromThread();
+}
+
+ModelTypeStoreBackend::~ModelTypeStoreBackend() {
+  DCHECK(CalledOnValidThread());
+}
+
+ModelTypeStore::Result ModelTypeStoreBackend::Init() {
+  DCHECK(CalledOnValidThread());
+  return ModelTypeStore::Result::SUCCESS;
+}
+
+}  // namespace syncer_v2