Consider this UMA stat (Google only):

https://uma.googleplex.com/p/chrome/timeline_v2/?sid=d5c32a2c84b5d502e6b55073b60df550

It shows a lot of usage of MediaStreamConstraintsFromDictionary, which is very old and obsolete, and really shouldn't happen.

Code inspection shows that it can be called not only from "new RTCPeerConnection", but also from AddStream, CreateOffer and CreateAnswer.

Some of these are Optional; if they're missing or empty, we shouldn't count them.

Also, we could remove the argument from AddStream. In AddStream, the only thing we do with them is print a warning that they're not supported. (The AddStream function is removed from the spec, so spec compliance is not an issue.)