Updating RTCQuicTransport onstatechange event to Promise

[shampson]

The state for the RTCQuicStream has been updated, but what about the RTCQuicTransport? The event currently fires for the following asynchronous cases:

• transitioning from connecting --> connected
• transitioning from connected --> failed
• transitioning from connected --> closed

Why not use a Promise and remove the event because these are fire once events?
https://developers.google.com/web/fundamentals/primers/promises#events_arent_always_the_best_way

// Resolves when transport is closed due to a failure/errror or stop() being called on
// the remote side. Both of these mean a CONNECTION_CLOSE frame.
readonly attribute Promise<RTCQuicTransportStopInfo> transportClosed;
// Resolves when transport becomes connected.
readonly attribute Promise<void> transportConnected;

Without doing this or at least having an onstopped specific event for the Transport, the following PR isn't really useful:

• PR 82 (Allows specifying errorCode with stop()).
• Resolving issue 62

I would prefer not to add another onstopped specific event (now we again have two potential events that can fire for one event occurring). This would also fix issue 42, which fires two events for receiving an error (onstatechange connected-->failed & onerror).

[shampson]

Note - I'm going to think about this more and come back to it.

[shampson]

Update:
The CONNECTION_CLOSE frame has two types:

• 0x1c for the QUIC layer, with transport error codes
• 0x1d for the application layer, which manages its own protocol space for error codes

This promise based solution could be:

readonly attribute Promise<void> transportConnected;
readonly attribute Promise<RTCQuicRemoteTransportCloseInfo> remoteTransportClosed;

dictionary QuicTransportRemoteCloseInfo {
   // Application or QUIC level error code.
   unsigned short errorCode = 0;
   DOMString      reason = "";
   RemoteCloseType type;
};

enum RemoteCloseType {
  "application-stop",
  "quic-error"
}

I'll open a separate issue regarding the fix to include the StopInfo from stop() on the remote side and reference it here.