sync: Introduce control data types

sync/internal_api/public/engine/control_model_worker.h

Index: sync/internal_api/public/engine/control_model_worker.h
diff --git a/sync/internal_api/public/engine/control_model_worker.h b/sync/internal_api/public/engine/control_model_worker.h
new file mode 100644
index 0000000000000000000000000000000000000000..20e5488bc29c6fbc6839e1c54370cace4d9b77fc
--- /dev/null
+++ b/sync/internal_api/public/engine/control_model_worker.h
@@ -0,0 +1,40 @@
+// 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_INTERNAL_API_PUBLIC_ENGINE_CONTROL_MODEL_WORKER_H_
+#define SYNC_INTERNAL_API_PUBLIC_ENGINE_CONTROL_MODEL_WORKER_H_
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "sync/base/sync_export.h"
+#include "sync/internal_api/public/engine/model_safe_worker.h"
+#include "sync/internal_api/public/util/syncer_error.h"
+
+class MessageLoop;
+
+namespace syncer {
+
+// Implementation of ModelSafeWorker for control types.  All work is
+// done on the same thread DoWorkAndWaitUntilDone (i.e., the sync
+// thread).
+class SYNC_EXPORT ControlModelWorker : public ModelSafeWorker {
+ public:
+  explicit ControlModelWorker(const MessageLoop* sync_loop);
+
+  // ModelSafeWorker implementation. Called on the sync thread.
+  virtual SyncerError DoWorkAndWaitUntilDone(
+      const WorkCallback& work) OVERRIDE;
+  virtual ModelSafeGroup GetModelSafeGroup() OVERRIDE;
+
+ private:
+  virtual ~ControlModelWorker();
+
+  const MessageLoop* const sync_loop_;
+
+  DISALLOW_COPY_AND_ASSIGN(ControlModelWorker);
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_INTERNAL_API_PUBLIC_ENGINE_CONTROL_MODEL_WORKER_H_