src/vs/workbench/api/common/extHostTypes.ts/NotebookCellOutputItem/error
class NotebookCellOutputItem:	static error(err: Error | { name: string, message?: string, stack?: string }): NotebookCellOutputItem {
		const obj = {
			name: err.name,
			message: err.message,
			stack: err.stack
		};
		return NotebookCellOutputItem.json(obj, 'application/vnd.code.notebook.error');
	}