This is in preparation for splitting MediaChannel into sender and receiver channels, with independent objects. Bug: webrtc:13931 Change-Id: I8e34b0c80b4d76132394efcda658a8face3ab873 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/288750 Reviewed-by: Henrik Boström <hbos@webrtc.org> Commit-Queue: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/main@{#38998}