Makes the new task queue based congestion controller implement the SendSideCongestionControllerInterface. Bug: webrtc:8415 Change-Id: I3dfe11c2eb200bc8d85c83edf78d7fdd0129bbff Reviewed-on: https://webrtc-review.googlesource.com/56781 Commit-Queue: Sebastian Jansson <srte@webrtc.org> Reviewed-by: Björn Terelius <terelius@webrtc.org> Cr-Commit-Position: refs/heads/master@{#22235}