Added Aura notification that relaunch and powerwash is required in case of downgrade.

ash/system/tray/system_tray_notifier.cc

Index: ash/system/tray/system_tray_notifier.cc
diff --git a/ash/system/tray/system_tray_notifier.cc b/ash/system/tray/system_tray_notifier.cc
index 1a55f8a1af8731457174bcf5eebbee9922eaba81..94fbc7520d2faaa32744f7e4bb746d68f5a4c5c5 100644
--- a/ash/system/tray/system_tray_notifier.cc
+++ b/ash/system/tray/system_tray_notifier.cc
@@ -285,11 +285,9 @@ void SystemTrayNotifier::NotifyLocaleChanged(
       OnLocaleChanged(delegate, cur_locale, from_locale, to_locale));
 }
 
-void SystemTrayNotifier::NotifyUpdateRecommended(
-    UpdateObserver::UpdateSeverity severity) {
-  FOR_EACH_OBSERVER(UpdateObserver,
-                    update_observers_,
-                    OnUpdateRecommended(severity));
+void SystemTrayNotifier::NotifyUpdateRecommended(const UpdateInfo& info) {
+  FOR_EACH_OBSERVER(
+      UpdateObserver, update_observers_, OnUpdateRecommended(info));
 }
 
 void SystemTrayNotifier::NotifyUserUpdate() {