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

ash/system/user/update_observer.h

Index: ash/system/user/update_observer.h
diff --git a/ash/system/user/update_observer.h b/ash/system/user/update_observer.h
index e509f62d3cb31461a1ba671d7478cbf4a79f9f5e..dacf1984dd20d568563bba8d9252d60aaa5c8745 100644
--- a/ash/system/user/update_observer.h
+++ b/ash/system/user/update_observer.h
@@ -9,18 +9,13 @@
 
 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