Introduce ash mojo interface for lock screen action handlers

ash/public/interfaces/tray_action.mojom

+// 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.
+
+module ash.mojom;
+
+// An action handler state.
+enum TrayActionState {
+  // The client does not support the action.
+  kNotSupported,
+
+  // The client supports the action, but the action cannot be handled at the
+  // moment, for example due to user session not being locked.
+  kNotAvailable,
+  
+  // The client supports the action and is not currently handling the action.
+  kAvailable,
+
+  // The client received the request for the action and it is launching the
+  // flow to handle it.
+  kLaunching,
+
+  // The client is currently handling the action.
+  kActive,
+
+  // The client is currently handling the action, but in background (e.g.
+  // handler window for lock screen action was moved to the background to
+  // surfeace user sign-in UI).
+  kBackground,
+};
+
+// Used by a client (e.g. Chrome) to notify ash of tray action handlers’ 
+// state changes.
+interface TrayAction {
+   // Sets the client to be used to handle action requests.
+   SetClient(TrayActionClient action_handler);

[xiyuan, 2017/05/04 21:19:16]

nit: wrong intent

[tbarzic, 2017/05/04 23:27:18]

Done.

+
+  // Updates action state for the lock screen note action. If called with no
+  // client set, the state change will not take effect until a client is set.
+  // Null client is equivalent to kNoteSupported state.
+  UpdateLockScreenNoteState(TrayActionState state);
+};
+
+// Used by ash to request Chrome to handle an action.
+interface TrayActionClient {
+  // Requests a lock screen note action to be handled.
+  RequestNewLockScreenNote();
+};