mash: Remove shelf app menu item objects.

ash/shell/window_watcher_shelf_item_delegate.cc

Index: ash/shell/window_watcher_shelf_item_delegate.cc
diff --git a/ash/shell/window_watcher_shelf_item_delegate.cc b/ash/shell/window_watcher_shelf_item_delegate.cc
index 99d69ec757dbd5b5b82862be2c1816379509ac6c..d7cd2424b13aa3adafd595a4e2f1cb63e39b0625 100644
--- a/ash/shell/window_watcher_shelf_item_delegate.cc
+++ b/ash/shell/window_watcher_shelf_item_delegate.cc
@@ -40,6 +40,12 @@ ShelfAppMenuItemList WindowWatcherShelfItemDelegate::GetAppMenuItems(
   return ShelfAppMenuItemList();
 }
 
+void WindowWatcherShelfItemDelegate::ExecuteCommand(uint32_t command_id,
+                                                    int event_flags) {
+  // This delegate does not support showing an application menu.
+  NOTIMPLEMENTED();
+}
+
 void WindowWatcherShelfItemDelegate::Close() {}
 
 }  // namespace shell