Add data for RTCIceCandidatePairStats (#3628)
Add data for RTCIceCandidatePairStats (#3628)

* More updates for RTCIceCandidatePeerStats

* Further progress on RTCIceCandidatePairStats (note the name is
corrected)

* RTCIceCandidatePairStats: Finish adding data
This commit adds the remaining Firefox and Chrome data that I will
include for the first push of this interface to BCD. Any additional
data, other than corrections to blatant errors or Firefox specific
issues, can be done in a follow-up.

* https://bugzilla.mozilla.org/show_bug.cgi?id=906990 (Firefox 29)
* https://bugzilla.mozilla.org/show_bug.cgi?id=1339906 (Firefox 56)

https://bugs.chromium.org/p/chromium/issues/detail?id=633550
https://bugs.chromium.org/p/chromium/issues/detail?id=627816
https://bugs.chromium.org/p/webrtc/issues/detail?id=7062&desc=3
https://chromium.googlesource.com/chromium/src/+/6c227da7f61037394fa95f3d071c4af3827e3a8e

* Set Chrome version for the RTCIceCandidatePairStats dict
jpmedley says this seems to have arrived in Chrome 56.

chrisdavidmills/browser-compat-data,chrisdavidmills/browser-compat-data,mdn/browser-compat-data,mdn/browser-compat-data