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

ash/common/system/update/tray_update.h

Index: ash/common/system/update/tray_update.h
diff --git a/ash/common/system/update/tray_update.h b/ash/common/system/update/tray_update.h
index 5cf23f7002701f4e9837b28117fe9aaf4a2c23b5..93136baa294cbba29f4dcf02c70efbede2594a43 100644
--- a/ash/common/system/update/tray_update.h
+++ b/ash/common/system/update/tray_update.h
@@ -8,6 +8,7 @@
 #include "ash/ash_export.h"
 #include "ash/common/system/tray/tray_image_item.h"
 #include "ash/common/system/update/update_observer.h"
+#include "ash/public/interfaces/update.mojom.h"
 #include "base/macros.h"
 
 namespace views {
@@ -16,19 +17,28 @@ class View;
 
 namespace ash {
 
-// The system update tray item. Exported for test.
+// The system update tray item. The tray icon stays visible once an update
+// notification is received. The icon only disappears after a reboot to apply
+// the update. Exported for test.
 class ASH_EXPORT TrayUpdate : public TrayImageItem, public UpdateObserver {
  public:
   explicit TrayUpdate(SystemTray* system_tray);
   ~TrayUpdate() override;
 
  private:
+  class UpdateView;
+
   // Overridden from TrayImageItem.
   bool GetInitialVisibility() override;
   views::View* CreateDefaultView(LoginStatus status) override;
 
   // Overridden from UpdateObserver.
-  void OnUpdateRecommended(const UpdateInfo& info) override;
+  void ShowUpdateIcon(mojom::UpdateSeverity severity,
+                      bool factory_reset_required) override;
+
+  bool update_required_ = false;
+  mojom::UpdateSeverity severity_ = mojom::UpdateSeverity::NONE;
+  bool factory_reset_required_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(TrayUpdate);
 };