Use OnceCallback on Mojo interfaces in //ash

ash/shelf/app_list_shelf_item_delegate.h

Index: ash/shelf/app_list_shelf_item_delegate.h
diff --git a/ash/shelf/app_list_shelf_item_delegate.h b/ash/shelf/app_list_shelf_item_delegate.h
index 495e0351d6b6fa477a420ec132a68145348f7fa6..e0ca704b10f4aab470ee87296a1378f5d03c65ff 100644
--- a/ash/shelf/app_list_shelf_item_delegate.h
+++ b/ash/shelf/app_list_shelf_item_delegate.h
@@ -25,7 +25,7 @@ class AppListShelfItemDelegate : public ShelfItemDelegate {
   void ItemSelected(std::unique_ptr<ui::Event> event,
                     int64_t display_id,
                     ShelfLaunchSource source,
-                    const ItemSelectedCallback& callback) override;
+                    ItemSelectedCallback callback) override;
   void ExecuteCommand(uint32_t command_id, int32_t event_flags) override;
   void Close() override;