Missing fields in MediaTrackConstraints

[sk-]

The fields autoGainControl, noiseSupression, latency and channelCount defined in the spec https://w3c.github.io/mediacapture-main/getusermedia.html#media-track-constraints are missing from MediaTrackConstraints.

[mhegazy]

A PR would be appreciated.

[chris-morgan]

Note that only channelCount and latency are in the current Candidate Recommendation—​autoGainControl and noiseSuppression are only in the Working Draft. Not sure quite what protocol is in such cases, given that these are extra fields rather than types.