Moves ownership of the RtpSenders/RtpReceivers/BaseChannels to
RtpTransceiver objects. For now, there can only be one
RtpTransceiver for audio and one for video. Future work to
implement Unified Plan will relax this restriction.
Bug: webrtc:7600
Change-Id: I9dfe324de61e2b363948858da72624396e27fc1a
Reviewed-on: https://webrtc-review.googlesource.com/21461
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Peter Thatcher <pthatcher@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20802}