This prepares for adding unit tests for VideoSendStreamImpl.
Bug: None
Change-Id: I488041b09f4a455ce4cf1bdc7b8163ef6ad19a8a
Reviewed-on: https://webrtc-review.googlesource.com/70782
Reviewed-by: Benjamin Wright <benwright@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22926}
