Use OnceCallback on Mojo interfaces in //ash

ash/shelf/app_list_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/shelf/app_list_shelf_item_delegate.h"
 
+#include <utility>
+
 #include "ash/shelf/shelf_model.h"
 #include "ash/shell.h"
 #include "ash/strings/grit/ash_strings.h"
 #include "base/memory/ptr_util.h"
 #include "ui/app_list/app_list_switches.h"
 #include "ui/base/l10n/l10n_util.h"
 
 namespace ash {
 
 namespace {
@@ skipping 17 matching lines @@
   // Create an AppListShelfItemDelegate for that item.
   model->SetShelfItemDelegate(item.id,
                               base::MakeUnique<AppListShelfItemDelegate>());
 }
 
 AppListShelfItemDelegate::AppListShelfItemDelegate()
     : ShelfItemDelegate(ShelfID(kAppListId)) {}
 
 AppListShelfItemDelegate::~AppListShelfItemDelegate() {}
 
-void AppListShelfItemDelegate::ItemSelected(
-    std::unique_ptr<ui::Event> event,
-    int64_t display_id,
-    ShelfLaunchSource source,
-    const ItemSelectedCallback& callback) {
+void AppListShelfItemDelegate::ItemSelected(std::unique_ptr<ui::Event> event,
+                                            int64_t display_id,
+                                            ShelfLaunchSource source,
+                                            ItemSelectedCallback callback) {
   Shell::Get()->ToggleAppList();
-  callback.Run(SHELF_ACTION_APP_LIST_SHOWN, base::nullopt);
+  std::move(callback).Run(SHELF_ACTION_APP_LIST_SHOWN, base::nullopt);

[James Cook, 2017/05/09 18:30:40]

Aside: I know this decision has already been made, but I find the fact that you
have to std::move(callback) to run it to be difficult to read.

However, I'm glad to see there's a nice static assert telling you what to do
when you accidentally type callback.Run() without std::move(). Kudos to whoever
added that.

[tzik, 2017/05/11 08:15:20]

Yes, it's very helpful. Kudos goes to dcheng.

 }
 
 void AppListShelfItemDelegate::ExecuteCommand(uint32_t command_id,
                                               int32_t event_flags) {
   // This delegate does not support showing an application menu.
   NOTIMPLEMENTED();
 }
 
 void AppListShelfItemDelegate::Close() {}
 
 }  // namespace ash