UpdatePacingRates required that a bandwidth estimate was available and
would otherwise crash. This CL ensures that there is an initial bandwidth
estimate available from the beginning.
Bug: webrtc:8415
Change-Id: I20c3b444eac42326a78cfebee70b4c1aa370c867
Reviewed-on: https://webrtc-review.googlesource.com/69802
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22857}