Introduce ash mojo interface for lock screen action handlers

ash/tray_action_handler/tray_action_handler_observer.h

+// Copyright 2017 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 ASH_TRAY_ACTION_HANDLER_TRAY_ACTION_HANDLER_OBSERVER_H_
+#define ASH_TRAY_ACTION_HANDLER_TRAY_ACTION_HANDLER_OBSERVER_H_
+
+#include "ash/ash_export.h"

[James Cook, 2017/05/03 23:31:51]

not needed?

[tbarzic, 2017/05/04 20:58:31]

Done.

+
+#include "ash/public/interfaces/tray_action_handler.mojom.h"
+
+namespace ash {
+
+class TrayActionHandlerObserver {

[James Cook, 2017/05/03 23:31:51]

This doesn't look used - do you need it for a follow up CL?

[tbarzic, 2017/05/04 20:58:31]

yes, it's needed for a follow-up cl

+ public:
+  virtual ~TrayActionHandlerObserver() {}
+
+  // Called when action handler state changes.
+  virtual void OnActionStateChanged(mojom::TrayActionHandlerAction action,
+                                    mojom::TrayActionHandlerState state) = 0;
+};
+
+}  // namespace ash
+
+#endif  // ASH_TRAY_ACTION_HANDLER_TRAY_ACTION_HANDLER_OBSERVER_H_