This adds RtpTransceiver.StopStandard(), which behaves according to the specification at https://w3c.github.io/webrtc-pc/#dom-rtcrtptransceiver-stop It modifies RTCPeerConnection.getTransceivers() to return only transceivers that have not been stopped. Rebase of armax' https://webrtc-review.googlesource.com/c/src/+/172762 Bug: chromium:980879 Change-Id: I7d383ee874ccc0a006fdcf280496b5d4235425ce Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/180580 Reviewed-by: Kári Helgason <kthelgason@webrtc.org> Reviewed-by: Sami Kalliomäki <sakal@webrtc.org> Reviewed-by: Guido Urdaneta <guidou@webrtc.org> Commit-Queue: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/master@{#31893}