This ensures that the MediaChannel interface is only implemented through a send/receive shim, splitting channels also when kBoth is used. Bug: webrtc:13931 Change-Id: Ie97809597eaae7b4f504939339795432c34e56cb Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/307461 Reviewed-by: Henrik Boström <hbos@webrtc.org> Commit-Queue: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/main@{#40210}