Definition
WebRTC: Real-Time Communication in Browsers defines RTCTrackEvent
[Exposed=Window]
interface RTCTrackEvent : Event {
constructor(DOMString type, RTCTrackEventInit eventInitDict);
readonly attribute RTCRtpReceiver receiver;
readonly attribute MediaStreamTrack track;
[SameObject] readonly attribute FrozenArray<MediaStream> streams;
readonly attribute RTCRtpTransceiver transceiver;
};