Add update available icon in system tray

ash/system/update/tray_update.h

Index: ash/system/update/tray_update.h
diff --git a/ash/system/update/tray_update.h b/ash/system/update/tray_update.h
index 6d3a9c001ed08bafebe8d7d6e15af165e262e8c6..ca7f06f578f66bcf998bf940f8d01ee6ec9f8a29 100644
--- a/ash/system/update/tray_update.h
+++ b/ash/system/update/tray_update.h
@@ -38,6 +38,11 @@ class ASH_EXPORT TrayUpdate : public TrayImageItem {
                       bool factory_reset_required,
                       mojom::UpdateType update_type);
 
+  // Shows an icon in the system tray indicating that a software update is
+  // available but user's agreement is required as current connection is
+  // cellular. Once shown the icon persists until reboot.
+  void ShowUpdateOverCellularAvailableIcon();
+
  private:
   FRIEND_TEST_ALL_PREFIXES(TrayUpdateTest, VisibilityAfterUpdate);
   FRIEND_TEST_ALL_PREFIXES(TrayUpdateTest, VisibilityAfterFlashUpdate);
@@ -60,6 +65,7 @@ class ASH_EXPORT TrayUpdate : public TrayImageItem {
   static mojom::UpdateSeverity severity_;
   static bool factory_reset_required_;
   static mojom::UpdateType update_type_;
+  static bool update_over_cellular_available_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayUpdate);
 };