Ash: Fix browser icon menu model lifetime

ash/shelf/shelf_view.h

Index: ash/shelf/shelf_view.h
diff --git a/ash/shelf/shelf_view.h b/ash/shelf/shelf_view.h
index f68e959945704915d41b1e538bb7e45da0da0cfb..1635cb343fae560035538677d492ae1cf6c0d769 100644
--- a/ash/shelf/shelf_view.h
+++ b/ash/shelf/shelf_view.h
@@ -136,6 +136,7 @@ class ASH_EXPORT ShelfView : public views::View,
   const views::ViewModel* const view_model_for_test() const {
     return view_model_.get();
   }
+  ui::MenuModel* list_menu_model_for_test() { return list_menu_model_.get(); }
 
  private:
   friend class ash::test::ShelfViewTestAPI;