createSession method
Implementation
Future<WorkerSession> createSession([dynamic initial]) async {
var s = generateBasicId(length: 25);
var session = _WorkerSession(this, s, true, initial);
_sendPort.send(<String, dynamic>{
't': 'session.created',
's': s,
'n': initial,
});
await ((_sessionReady[s] = Completer<void>.sync()).future);
_ourSessions[s] = session;
return session;
}