ValueConnectableStream<T>.seeded  constructor 
Constructs a Stream which only begins emitting events when the connect method is called, this Stream acts like a BehaviorSubject.seeded.
Implementation
ValueConnectableStream.seeded(Stream<T> source, T seedValue,
    {bool sync = false})
    : super(source, BehaviorSubject<T>.seeded(seedValue, sync: sync));