Use OnceCallback on Mojo interfaces in //ash

ash/shell/window_watcher_shelf_item_delegate.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/shell/window_watcher_shelf_item_delegate.h"
 
+#include <utility>
+
 #include "ash/shell/window_watcher.h"
 #include "ash/wm/window_util.h"
 #include "ui/aura/window.h"
 
 namespace ash {
 namespace shell {
 
 WindowWatcherShelfItemDelegate::WindowWatcherShelfItemDelegate(
     ShelfID id,
     WindowWatcher* watcher)
     : ShelfItemDelegate(id), watcher_(watcher) {
   DCHECK(!id.IsNull());
   DCHECK(watcher_);
 }
 
 WindowWatcherShelfItemDelegate::~WindowWatcherShelfItemDelegate() {}
 
 void WindowWatcherShelfItemDelegate::ItemSelected(
     std::unique_ptr<ui::Event> event,
     int64_t display_id,
     ShelfLaunchSource source,
-    const ItemSelectedCallback& callback) {
+    ItemSelectedCallback callback) {
   aura::Window* window = watcher_->GetWindowByID(shelf_id());
   if (window->type() == ui::wm::WINDOW_TYPE_PANEL)
     wm::MoveWindowToDisplay(window, display_id);
   window->Show();
   wm::ActivateWindow(window);
-  callback.Run(SHELF_ACTION_WINDOW_ACTIVATED, base::nullopt);
+  std::move(callback).Run(SHELF_ACTION_WINDOW_ACTIVATED, base::nullopt);
 }
 
 void WindowWatcherShelfItemDelegate::ExecuteCommand(uint32_t command_id,
                                                     int32_t event_flags) {
   // This delegate does not support showing an application menu.
   NOTIMPLEMENTED();
 }
 
 void WindowWatcherShelfItemDelegate::Close() {}
 
 }  // namespace shell
 }  // namespace ash