ash: Use system tray mojo interface to show system update tray icon

ash/common/system/tray/system_tray_controller.cc

Index: ash/common/system/tray/system_tray_controller.cc
diff --git a/ash/common/system/tray/system_tray_controller.cc b/ash/common/system/tray/system_tray_controller.cc
index 659cd531d79de85487ef187c8ceb0328dc34f3dd..b9b86cca05c2e2f54964cb70a3d8cc4214d09ea3 100644
--- a/ash/common/system/tray/system_tray_controller.cc
+++ b/ash/common/system/tray/system_tray_controller.cc
@@ -128,4 +128,10 @@ void SystemTrayController::SetUse24HourClock(bool use_24_hour) {
   WmShell::Get()->system_tray_notifier()->NotifyDateFormatChanged();
 }
 
+void SystemTrayController::ShowUpdateIcon(mojom::UpdateSeverity severity,
+                                          bool factory_reset_required) {
+  WmShell::Get()->system_tray_notifier()->ShowUpdateIcon(
+      severity, factory_reset_required);
+}
+
 }  // namespace ash