[webrtc-stats] Stats for the delay of packets being sent (#420)

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

== Stats for the delay of packets being sent ==
Proposal: A metric that measures the time between each packet being produced and it being sent onto the network.
This is similar to jitter buffer delay but for the sender.

Please view or discuss this issue at https://github.com/w3c/webrtc-stats/issues/420 using your GitHub account