mus: Add UserActivityMonitor.

components/mus/public/interfaces/user_activity_monitor.mojom

+// Copyright 2016 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 mus.mojom;
+
+interface UserActivityObserver {
+  OnUserActivity();
+};
+
+interface UserIdleObserver {
+  enum IdleState {
+    ACTIVE,
+    IDLE,
+  };
+  OnUserIdleStateChanged(IdleState new_state);
+};
+
+interface UserActivityMonitor {
+  // Notifies the observer of user activity at most once every
+  // |delay_between_notify_secs| seconds.
+  AddUserActivityObserver(uint32 delay_between_notify_secs,
+                          UserActivityObserver observer);
+
+  // Notifies the observer when user is idle for more than
+  // |idle_time_in_minutes| minutes. When the observer is first added, if the
+  // user has already been idle for |idle_time_in_minutes|, then
+  // OnUserIdleStateChanged(IDLE) is called on the observer, otherwise
+  // OnUserIdleStateChanged(ACTIVE) is called.
+  AddUserIdleObserver(uint32 idle_time_in_minutes, UserIdleObserver observer);
+};