FYI: Control Data + Per-Device Metadata

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 {

[rlarocque, 2012/08/11 01:31:52]

This code is copy/pasted from PassiveModelWorker.  I feel sort of bad about
that.  

On the other hand, it would require much more code to define a 'BaseModelWorker'
and have both the PassiveModelWorker and ControlModelWorker inherit from it. 
This would enable us to share roughly two lines of actual code between both
classes.  It just doesn't seem worth the effort.

+ 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_