addStream method
Adds a stream directly the underlying response.
If this instance has access to a correspondingRequest, then it will attempt to transform the content using at most one of the response encoders.
Implementation
@override
Future addStream(Stream<List<int>> stream) async {
if (!isOpen && isBuffered) throw ResponseContext.closed();
// A buffered response is sent as a whole by the driver, so do not send
// headers now; add() appends to the buffer.
if (!isBuffered) await _commitOrThrow();
await stream.forEach(add);
}