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

ash/system/user/update_observer.h

 // 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.
 
 #ifndef ASH_SYSTEM_USER_UPDATE_OBSERVER_H_
 #define ASH_SYSTEM_USER_UPDATE_OBSERVER_H_
 
 #include "ash/ash_export.h"
 
 namespace ash {
 
+struct UpdateInfo;
+
 class ASH_EXPORT UpdateObserver {
  public:
-  enum UpdateSeverity {
-    UPDATE_NORMAL,
-    UPDATE_LOW_GREEN,
-    UPDATE_HIGH_ORANGE,
-    UPDATE_SEVERE_RED,
-  };
-
   virtual ~UpdateObserver() {}
 
-  virtual void OnUpdateRecommended(UpdateSeverity severity) = 0;
+  virtual void OnUpdateRecommended(const UpdateInfo& info) = 0;
 };
 
 }  // namespace ash
 
 #endif  //ASH_SYSTEM_USER_UPDATE_OBSERVER_H_