mash: Cleanup ash shelf application menu code.

ash/common/shelf/shelf_window_watcher_item_delegate.cc

Index: ash/common/shelf/shelf_window_watcher_item_delegate.cc
diff --git a/ash/common/shelf/shelf_window_watcher_item_delegate.cc b/ash/common/shelf/shelf_window_watcher_item_delegate.cc
index dfee1468c1af931186b0a7edcdf7dce1409d3ee9..6626a9c42a8f811ea2ba65c88b066078f6655b34 100644
--- a/ash/common/shelf/shelf_window_watcher_item_delegate.cc
+++ b/ash/common/shelf/shelf_window_watcher_item_delegate.cc
@@ -55,9 +55,9 @@ ShelfItemDelegate::PerformedAction ShelfWindowWatcherItemDelegate::ItemSelected(
   return kExistingWindowActivated;
 }
 
-ui::SimpleMenuModel* ShelfWindowWatcherItemDelegate::CreateApplicationMenu(
+ShelfApplicationMenuItems ShelfWindowWatcherItemDelegate::GetAppMenuItems(
     int event_flags) {
-  return nullptr;
+  return ShelfApplicationMenuItems();
 }
 
 void ShelfWindowWatcherItemDelegate::Close() {