This allows us to decouple implementation classes from the MediaChannel class. Bug: webrtc:13931 Change-Id: I22f166cac17c344f943a0382048e8086a193affa Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/307000 Commit-Queue: Harald Alvestrand <hta@webrtc.org> Reviewed-by: Henrik Boström <hbos@webrtc.org> Cr-Commit-Position: refs/heads/main@{#40179}