Support SystemTrayDelegate::ShowPowerSettings() in mustash

ash/public/interfaces/system_tray.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 ash.mojom;
 
 // Allows clients (e.g. Chrome browser) to control the ash system tray menu.
 interface SystemTray {
   // Sets the clock to use 24 hour time formatting if |use_24_hour| is true.
   // Otherwise sets 12 hour time formatting.
   SetUse24HourClock(bool use_24_hour);
 };
 
 // Allows ash system tray to control a client (e.g. Chrome browser). Requests
 // often involve preferences or web UI that is not available to ash.
 interface SystemTrayClient {
   // Shows general settings UI.
   ShowSettings();
 
   // Shows the settings related to date, timezone etc.
   ShowDateSettings();
 
   // TODO(crbug.com/647412): ShowSetTimeDialog();
 
   // TODO(crbug.com/647412): ShowNetworkSettingsForGuid(string guid);
 
   // Shows settings related to multiple displays.
   ShowDisplaySettings();
 
-  // TODO(crbug.com/647412): ShowPowerSettings();
+  // Shows settings related to power.
+  ShowPowerSettings();
 
   // Shows the page that lets you disable performance tracing.
   ShowChromeSlow();
 
   // Shows settings related to input methods.
   ShowIMESettings();
 
   // Shows help.
   ShowHelp();
 
@@ skipping 10 matching lines @@
   ShowPaletteSettings();
 
   // Shows information about public account mode.
   ShowPublicAccountInfo();
 
   // TODO(crbug.com/647412): ShowEnterpriseInfo();
 
   // Shows UI for changing proxy settings.
   ShowProxySettings();
 };