StreamChannel<T>  constructor 
- Stream<T> stream,
- StreamSink<T> sink
Creates a new StreamChannel that communicates over stream and sink.
Note that this stream/sink pair must provide the guarantees listed in the StreamChannel documentation. If they don't do so natively, StreamChannel.withGuarantees should be used instead.
Implementation
factory StreamChannel(Stream<T> stream, StreamSink<T> sink) =>
    _StreamChannel<T>(stream, sink);