This makes the channel manager object into a factory, not a manager. Bug: webrtc:13931 Change-Id: I59f7d818a739797a7c0a7a32e6583450834df122 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/260467 Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org> Commit-Queue: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/main@{#36718}