Use OnceCallback on Mojo interfaces in //ash

ash/shelf/shelf_view_unittest.cc

Index: ash/shelf/shelf_view_unittest.cc
diff --git a/ash/shelf/shelf_view_unittest.cc b/ash/shelf/shelf_view_unittest.cc
index 1d969cabbe815ceddc3f6a14f92b2d8bfbd2e6a5..c54d67d88b7b70cdaabb28bdd5b3dac4677eaa41 100644
--- a/ash/shelf/shelf_view_unittest.cc
+++ b/ash/shelf/shelf_view_unittest.cc
@@ -152,9 +152,9 @@ class ShelfItemSelectionTracker : public ShelfItemDelegate {
   void ItemSelected(std::unique_ptr<ui::Event> event,
                     int64_t display_id,
                     ShelfLaunchSource source,
-                    const ItemSelectedCallback& callback) override {
+                    ItemSelectedCallback callback) override {
     item_selected_count_++;
-    callback.Run(item_selected_action_, base::nullopt);
+    std::move(callback).Run(item_selected_action_, base::nullopt);
   }
   void ExecuteCommand(uint32_t command_id, int32_t event_flags) override {}
   void Close() override {}
@@ -2007,12 +2007,12 @@ class ListMenuShelfItemDelegate : public ShelfItemDelegate {
   void ItemSelected(std::unique_ptr<ui::Event> event,
                     int64_t display_id,
                     ShelfLaunchSource source,
-                    const ItemSelectedCallback& callback) override {
+                    ItemSelectedCallback callback) override {
     // Two items are needed to show a menu; the data in the items is not tested.
     std::vector<mojom::MenuItemPtr> items;
     items.push_back(mojom::MenuItem::New());
     items.push_back(mojom::MenuItem::New());
-    callback.Run(SHELF_ACTION_NONE, std::move(items));
+    std::move(callback).Run(SHELF_ACTION_NONE, std::move(items));
   }
   void ExecuteCommand(uint32_t command_id, int32_t event_flags) override {}
   void Close() override {}