23425f9068
The point of this change is to make it possible to create the congestion controller as part of creating RtpTransportController, later pass it to the constructor of Call, and then let Call register itself as an observer. BUG=webrtc:7135 Review-Url: https://codereview.webrtc.org/2795643002 Cr-Commit-Position: refs/heads/master@{#17504}