[mediacapture-main] Pull Request: Add video latency constrainable property

kuddai has just submitted a new pull request for https://github.com/w3c/mediacapture-main:

== Add video latency constrainable property ==
We would like to extended existing [latency](https://www.w3.org/TR/mediacapture-streams/#def-constraint-latency) constrainable property API to the video case as well. For e.g. it will allow to adjust audio/video synchronization from the client code.

See https://github.com/w3c/mediacapture-main/pull/572