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

ash/system/tray/system_tray_notifier.cc

 // Copyright (c) 2012 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.
 
 #include "ash/system/tray/system_tray_notifier.h"
 
 #if defined(OS_CHROMEOS)
 #include "ash/system/chromeos/network/network_state_notifier.h"
 #endif
 
@@ skipping 267 matching lines @@
     LocaleObserver::Delegate* delegate,
     const std::string& cur_locale,
     const std::string& from_locale,
     const std::string& to_locale) {
   FOR_EACH_OBSERVER(
       LocaleObserver,
       locale_observers_,
       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() {
   FOR_EACH_OBSERVER(UserObserver,
                     user_observers_,
                     OnUserUpdate());
 }
 
 void SystemTrayNotifier::NotifyUserAddedToSession() {
   FOR_EACH_OBSERVER(UserObserver,
@@ skipping 77 matching lines @@
 
 void SystemTrayNotifier::NotifyLastWindowClosed() {
   FOR_EACH_OBSERVER(LastWindowClosedObserver,
                     last_window_closed_observers_,
                     OnLastWindowClosed());
 }
 
 #endif  // OS_CHROMEOS
 
 }  // namespace ash