This also changes AppRTC to use addTrack instead of addStream and
"early media" using the RtpTransceiver API.
Bug: webrtc:8870
Change-Id: Ie2848a87c71a95adb785367d822c61e1f753d8c6
Reviewed-on: https://webrtc-review.googlesource.com/56440
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22255}