src/vs/workbench/services/extensions/common/rpcProtocol.ts/MessageIO/_serializeReplyErrEror
class MessageIO:	private static _serializeReplyErrEror(req: number, _err: Error): VSBuffer {
		const errBuff = VSBuffer.fromString(safeStringify(errors.transformErrorForSerialization(_err), null));

		let len = 0;
		len += MessageBuffer.sizeLongString(errBuff);

		let result = MessageBuffer.alloc(MessageType.ReplyErrError, req, len);
		result.writeLongString(errBuff);
		return result.buffer;
	}