This is a preparation for deleting ChannelReceiveProxy, Changes
signature of some methods, and demotes methods OnData and
OnReceivedPayloadData to private.
Bug: webrtc:9801
Change-Id: Ib00a80c6482ed5238f3cc8233860c70f11484df9
Reviewed-on: https://webrtc-review.googlesource.com/c/110606
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25599}