This CL removes a couple more opportunities for client code to interact directly with the MediaChannel implementation classes. No-try because of infra failure. No-Try: true Bug: webrtc:13931 Change-Id: I658b8b04eff11de7831a1933d16d40fc59c3f0fc Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/288380 Commit-Queue: Harald Alvestrand <hta@webrtc.org> Reviewed-by: Henrik Boström <hbos@webrtc.org> Cr-Commit-Position: refs/heads/main@{#38935}