[Sync] Add ModelTypeStore implementation.

sync/internal_api/public/model_type_store_backend.h

Index: sync/internal_api/public/model_type_store_backend.h
diff --git a/sync/internal_api/public/model_type_store_backend.h b/sync/internal_api/public/model_type_store_backend.h
new file mode 100644
index 0000000000000000000000000000000000000000..cdbcd7b892bd6b44ec219ed50297b209a0ff7715
--- /dev/null
+++ b/sync/internal_api/public/model_type_store_backend.h
@@ -0,0 +1,26 @@
+// 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.
+
+#ifndef SYNC_INTERNAL_API_PUBLIC_MODEL_TYPE_STORE_BACKEND_H_
+#define SYNC_INTERNAL_API_PUBLIC_MODEL_TYPE_STORE_BACKEND_H_
+
+#include "base/threading/non_thread_safe.h"
+#include "sync/api/model_type_store.h"
+
+namespace syncer_v2 {
+
+// ModelTypeStoreBackend handles operations with leveldb. It is oblivious of the
+// fact that it is called from separate thread (with the exception of ctor),
+// meaning it shouldn't deal with callbacks and task_runners.
+class ModelTypeStoreBackend : public base::NonThreadSafe {
+ public:
+  ModelTypeStoreBackend();
+  ~ModelTypeStoreBackend();
+
+  ModelTypeStore::Result Init();
+};
+
+}  // namespace syncer_v2
+
+#endif  // SYNC_INTERNAL_API_PUBLIC_MODEL_TYPE_STORE_BACKEND_H_