Change WebRtcSession to have a vector of channels

This is the first step towards supporting multiple audio/video
channels in PeerConnection/WebRtcSession. For now, there can only
be 0 or 1 channels in the vector. This adds the framework so that
all the other code that assumes a single audio/video channel can
be transitioned one-by-one to multiple channels.

Bug: webrtc:8183
Change-Id: I6456af32d6e3adf7eb83e281e43253ea973c4eb9
Commit-Queue: Steve Anton <>
Reviewed-by: Taylor Brandstetter <>
Cr-Original-Commit-Position: refs/heads/master@{#19615}
Cr-Mirrored-Commit: 169629aca3140803731af3d586932ffc176bed46
2 files changed