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..2ab81c86522e339618e0c311cf4295852a8f4b76 100644
--- a/ash/common/shelf/shelf_window_watcher_item_delegate.cc
+++ b/ash/common/shelf/shelf_window_watcher_item_delegate.cc
@@ -55,9 +55,10 @@ ShelfItemDelegate::PerformedAction ShelfWindowWatcherItemDelegate::ItemSelected(
   return kExistingWindowActivated;
 }
 
-ui::SimpleMenuModel* ShelfWindowWatcherItemDelegate::CreateApplicationMenu(
+ShelfAppMenuItemList ShelfWindowWatcherItemDelegate::GetAppMenuItems(
     int event_flags) {
-  return nullptr;
+  // Return an empty item list to avoid showing an application menu.
+  return ShelfAppMenuItemList();
 }
 
 void ShelfWindowWatcherItemDelegate::Close() {