[Track Stats API] Feature detection of audio vs video stats

[henbos]

MediaStreamTrack can be either audio or video. We've previously talked about having a single stats method for both the audio and video case for consistency, but as I implemented a prototype of this API for video stats and not audio stats, I realized that if both APIs share the same name then there is no way to easily feature detect this API, unless you consider try-catch a sensible option and throwing in the not implemented case.

Proposal:

• Let's use different names, e.g. getAudioStats/getVideoStats if a method or audioStats/videoStats if an attribute.

[henbos]

Alternative discussed: just return an empty dictionary

[henbos]

In TPAC the desire to just call this "stats" was expressed (#107) and in a previous meeting there was little interest in feature detection, so I'm abandoning this issue