The following revision refers to this bug:
  https://chromium.googlesource.com/external/webrtc.git/+/09bc128603909680a3d9d09100d9be7d3f008036

commit 09bc128603909680a3d9d09100d9be7d3f008036
Author: hbos <hbos@webrtc.org>
Date: Tue Nov 08 14:29:22 2016

RTCMediaStream[Track]Stats added.

Not all members are collected by RTCStatsCollector and detached tracks
are not visible in the returned stats. This needs to be addressed before
closing  crbug.com/660827  and  crbug.com/659137 

BUG= chromium:660827 ,  chromium:659137 ,  chromium:627816 

Review-Url: https://codereview.webrtc.org/2467873005
Cr-Commit-Position: refs/heads/master@{#14978}

[modify] https://crrev.com/09bc128603909680a3d9d09100d9be7d3f008036/webrtc/api/rtcstatscollector.cc
[modify] https://crrev.com/09bc128603909680a3d9d09100d9be7d3f008036/webrtc/api/rtcstatscollector.h
[modify] https://crrev.com/09bc128603909680a3d9d09100d9be7d3f008036/webrtc/api/rtcstatscollector_unittest.cc
[modify] https://crrev.com/09bc128603909680a3d9d09100d9be7d3f008036/webrtc/api/stats/rtcstats_objects.h
[modify] https://crrev.com/09bc128603909680a3d9d09100d9be7d3f008036/webrtc/api/test/mock_peerconnection.h
[modify] https://crrev.com/09bc128603909680a3d9d09100d9be7d3f008036/webrtc/stats/rtcstats_objects.cc

Is this finished?

No.

Bumping this to M58. Please correct if that's wrong.

The stream stats are finished, what's missing is streams/tracks that have been detached, that is tracked by the webrtc bug for RTCMediaStreamTrackStats already, no need for a separate RTCMediaStreamStats bug. Closing using M-57 since the streams have been added with all members since then.