[webrtc-pc] Pull Request: "Hybrid" OAuth solution.

taylor-b has just submitted a new pull request for 
https://github.com/w3c/webrtc-pc:

== "Hybrid" OAuth solution. ==
Fixes #714.

The working group decided on this solution in the Jan 25 2017 virtual
interim. The "username" field will be used for the kid, and the other
two pieces of credential information will go in "credential". The 
reasoning
for this decision was that it's backwards compatible, and doesn't add
more fields to the RTCIceServer dictionary.

Based on earlier PR with @misi, with some minor editorial tweaks.

See https://github.com/w3c/webrtc-pc/pull/1033