[webrtc-stats] Stat for retransmitted bytes

henbos has just created a new issue for 
https://github.com/w3c/webrtc-stats:

== Stat for retransmitted bytes ==
The non-standardized Chromium getStats contains the following stat:
```
// The total retransmission bandwidth, in bits per second.
VideoBwe.googRetransmitBitrate
```
Is this useful? Should we add retransmitted bytes counters to the 
spec? We have bytesSent/bytesReceived on various stats dictionaries 
already: RTCTransportStats, RTCDataChannelStats, 
RTC[In/Out]boundRTPStreamStats and RTCIceCandidatePairStats. Does the 
existing bytesSent/bytesReceived include or exclude bytes that are 
retransmitted?

Please view or discuss this issue at 
https://github.com/w3c/webrtc-stats/issues/154 using your GitHub 
account