sync: Introduce control data types

sync/engine/apply_control_data_updates.h

+// Copyright (c) 2012 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_ENGINE_APPLY_CONTROL_DATA_UPDATES_H_
+#define SYNC_ENGINE_APPLY_CONTROL_DATA_UPDATES_H_
+
+namespace syncer {
+
+class Cryptographer;
+
+namespace syncable {
+class Directory;
+class WriteTransaction;
+}
+
+void ApplyControlDataUpdates(syncable::Directory* dir);
+bool ApplyNigoriUpdates(syncable::WriteTransaction* trans,
+                        Cryptographer* cryptographer);
+
+}  // namespace syncer
+
+#endif  // SYNC_ENGINE_APPLY_CONTROL_DATA_UPDATES_H_