Sync: Refactoring DataTypeController to make the design shareable with USS datatypes.

components/sync_driver/directory_data_type_controller.h

Index: components/sync_driver/directory_data_type_controller.h
diff --git a/components/sync_driver/directory_data_type_controller.h b/components/sync_driver/directory_data_type_controller.h
new file mode 100644
index 0000000000000000000000000000000000000000..67aa41ae82c79ba81869298b7208315e66caea22
--- /dev/null
+++ b/components/sync_driver/directory_data_type_controller.h
@@ -0,0 +1,43 @@
+// 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 COMPONENTS_SYNC_DRIVER_DIRECTORY_DATA_TYPE_CONTROLLER_H__
+#define COMPONENTS_SYNC_DRIVER_DIRECTORY_DATA_TYPE_CONTROLLER_H__
+
+#include "components/sync_driver/data_type_controller.h"
+
+#include "sync/internal_api/public/engine/model_safe_worker.h"
+
+namespace sync_driver {
+class ChangeProcessor;
+
+// Base class for Directory based Data type controllers.
+class DirectoryDataTypeController : public DataTypeController {
+ public:
+  // Activates this controller's data type.

[Nicolas Zea, 2015/09/02 22:52:45]

nit: would be good to explain a bit more about what these two methods involve,
and why they're something directory specific. Also worth calling out which
thread they're called on, since as I recall one of them is the UI thread, the
other is the datatype thread.

[stanisc, 2015/09/03 01:17:42]

Provided a bit more detailed comments here and in the base class.
I'll revise these comments once again when I'll have an alternative mechanism
for 
USS datatypes (which I think will be overloaded pair of methods on the
configurer).

+  void ActivateDataType(BackendDataTypeConfigurer* configurer) override;
+
+  // Deactivates this controller's data type.
+  void DeactivateDataType(BackendDataTypeConfigurer* configurer) override;
+
+ protected:
+  // The model safe group of this data type.  This should reflect the
+  // thread that should be used to modify the data type's native
+  // model.
+  virtual syncer::ModelSafeGroup model_safe_group() const = 0;
+
+  // Access to the ChangeProcessor for the type being controlled by |this|.
+  // Returns NULL if the ChangeProcessor isn't created or connected.
+  virtual ChangeProcessor* GetChangeProcessor() const = 0;
+
+  DirectoryDataTypeController(
+      scoped_refptr<base::SingleThreadTaskRunner> ui_thread,

[Nicolas Zea, 2015/09/02 22:52:45]

nit: pass scoped_refptrs by const ref ("const scoped_refptr<..>&")

[stanisc, 2015/09/03 01:17:42]

OK, changed here and in derived classes.

+      const base::Closure& error_callback);
+
+  ~DirectoryDataTypeController() override;
+};
+
+}  // namespace sync_driver
+
+#endif  // COMPONENTS_SYNC_DRIVER_DIRECTORY_DATA_TYPE_CONTROLLER_H__