Add update available icon in system tray

ash/public/interfaces/system_tray.mojom

Index: ash/public/interfaces/system_tray.mojom
diff --git a/ash/public/interfaces/system_tray.mojom b/ash/public/interfaces/system_tray.mojom
index f1108c49d4f0b7e209de134d65607456a0303627..1239a614a40196109aff2967d39d5e02a20d6a38 100644
--- a/ash/public/interfaces/system_tray.mojom
+++ b/ash/public/interfaces/system_tray.mojom
@@ -34,6 +34,11 @@ interface SystemTray {
   ShowUpdateIcon(UpdateSeverity severity,
                  bool factory_reset_required,
                  UpdateType update_type);
+
+  // Shows an icon in the system tray indicating that a software update is
+  // available but user's agreement is required as current connection is
+  // cellular. Once shown the icon persists until reboot.
+  ShowUpdateOverCellularAvailableIcon();
 };
 
 // Allows ash system tray to control a client (e.g. Chrome browser). Requests
@@ -72,6 +77,9 @@ interface SystemTrayClient {
   // Shows settings related to input methods.
   ShowIMESettings();
 
+  // Show the about chrome OS page.

[stevenjb, 2017/05/16 19:49:06]

Shows

[weidongg, 2017/05/17 00:27:23]

Done.

+  ShowAboutChromeOS();
+
   // Shows help.

[stevenjb, 2017/05/16 19:49:06]

Change this to: // Shows the Chromebook help app.

[weidongg, 2017/05/17 00:27:23]

Done.

   ShowHelp();
 
@@ -121,4 +129,7 @@ interface SystemTrayClient {
 
   // Attempts to restart the system for update.
   RequestRestartForUpdate();
+
+  // Schedule checking for update after about Chrome OS page is loaded.
+  ScheduleRequestUpdateCheck();
 };