src/vs/workbench/contrib/notebook/browser/services/notebookEditorServiceImpl.ts/NotebookEditorWidgetService/_createBorrowValue
class NotebookEditorWidgetService:	private _createBorrowValue(myToken: number, widget: { widget: NotebookEditorWidget; token: number | undefined }): IBorrowValue<NotebookEditorWidget> {
		return {
			get value() {
				return widget.token === myToken ? widget.widget : undefined;
			}
		};
	}