This will generate an all-zeroes track stat when the sender
has not yet been connected (SSRC has not been assigned).
Bug: webrtc:8673
Change-Id: Id59e6941bc87eba6bb33b4d2a8fd808d985052c7
Reviewed-on: https://webrtc-review.googlesource.com/43080
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Fredrik Solenberg <solenberg@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21734}
b8e1201020