Fix crash on openning settings when DCHECK is on.

ash/shelf/app_list_shelf_item_delegate.h

Index: ash/shelf/app_list_shelf_item_delegate.h
diff --git a/ash/shelf/app_list_shelf_item_delegate.h b/ash/shelf/app_list_shelf_item_delegate.h
index 495e0351d6b6fa477a420ec132a68145348f7fa6..5f1e703bd8a8e7385d1c3f4f1b60ec0a43e6a54a 100644
--- a/ash/shelf/app_list_shelf_item_delegate.h
+++ b/ash/shelf/app_list_shelf_item_delegate.h
@@ -18,6 +18,9 @@ class AppListShelfItemDelegate : public ShelfItemDelegate {
   // AppListShelfItemDelegate which will be owned by |model|.
   static void CreateAppListItemAndDelegate(ShelfModel* model);
 
+  // An app id for the app list, used to identify the shelf item.
+  static const char kAppListId[];
+
   AppListShelfItemDelegate();
   ~AppListShelfItemDelegate() override;