mash: Remove shelf app menu item objects.

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 2b56a38004a8ebeb08607d8ce27c5f503037a476..b04360b11b9c224339cf2e99218e0b25311d9bda 100644
--- a/ash/common/shelf/shelf_window_watcher_item_delegate.cc
+++ b/ash/common/shelf/shelf_window_watcher_item_delegate.cc
@@ -65,6 +65,12 @@ ShelfAppMenuItemList ShelfWindowWatcherItemDelegate::GetAppMenuItems(
   return ShelfAppMenuItemList();
 }
 
+void ShelfWindowWatcherItemDelegate::ExecuteCommand(uint32_t command_id,
+                                                    int32_t event_flags) {
+  // This delegate does not support showing an application menu.
+  NOTIMPLEMENTED();
+}
+
 void ShelfWindowWatcherItemDelegate::Close() {
   window_->CloseWidget();
 }