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

ash/common/system/tray/system_tray_notifier.h

Index: ash/common/system/tray/system_tray_notifier.h
diff --git a/ash/common/system/tray/system_tray_notifier.h b/ash/common/system/tray/system_tray_notifier.h
index 26e72d59c49088e6d7a823d6659887ef7f50be67..e313df185cceaf861b883ba1944e387fc01b5a28 100644
--- a/ash/common/system/tray/system_tray_notifier.h
+++ b/ash/common/system/tray/system_tray_notifier.h
@@ -22,8 +22,6 @@ namespace ash {
 class AccessibilityObserver;
 class ClockObserver;
 class IMEObserver;
-struct UpdateInfo;
-class UpdateObserver;
 class UserObserver;
 
 #if defined(OS_CHROMEOS)
@@ -40,6 +38,10 @@ class TracingObserver;
 class VirtualKeyboardObserver;
 #endif
 
+namespace mojom {
+enum class UpdateSeverity;
+}
+
 // Observer and notification manager for the ash system tray.
 class ASH_EXPORT SystemTrayNotifier {
  public:
@@ -66,11 +68,6 @@ class ASH_EXPORT SystemTrayNotifier {
   void NotifyRefreshIME();
   void NotifyRefreshIMEMenu(bool is_active);
 
-  // OS updates.
-  void AddUpdateObserver(UpdateObserver* observer);
-  void RemoveUpdateObserver(UpdateObserver* observer);
-  void NotifyUpdateRecommended(const UpdateInfo& info);
-
   // User.
   void AddUserObserver(UserObserver* observer);
   void RemoveUserObserver(UserObserver* observer);
@@ -147,7 +144,6 @@ class ASH_EXPORT SystemTrayNotifier {
   base::ObserverList<AccessibilityObserver> accessibility_observers_;
   base::ObserverList<ClockObserver> clock_observers_;
   base::ObserverList<IMEObserver> ime_observers_;
-  base::ObserverList<UpdateObserver> update_observers_;
   base::ObserverList<UserObserver> user_observers_;
 
 #if defined(OS_CHROMEOS)