This CL will be followed up with a CL adding AudioSendStream to
BitrateAllocator, so this is a small CL to have the video connection to
BitrateAllocator "at the same level" as for audio.
BUG=webrtc:5079
R=stefan@webrtc.org
Review URL: https://codereview.webrtc.org/1785283002 .
Cr-Commit-Position: refs/heads/master@{#11955}