This corresponds to processing the removal of a remote track step of
the spec, with processing the addition of a remote track already
covered by OnAddTrack.
https://w3c.github.io/webrtc-pc/#processing-remote-mediastreamtracks
Bug: webrtc:8260, webrtc:8315
Change-Id: Ica8be92369733eb3cf1397fb60385d45a9b58700
Reviewed-on: https://webrtc-review.googlesource.com/4722
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20214}