CL that landed a while ago, for some reason it did not show up on this issue:
https://codereview.webrtc.org/2242043002/

A TODO that needs to be addressed before closing this issue:
  // TODO(hbos): If data channels are removed from the peer connection this will
  // yield incorrect counts. Address before closing  crbug.com/636818 . See
  // https://w3c.github.io/webrtc-stats/webrtc-stats.html#pcstats-dict*.

The following revision refers to this bug:
  https://chromium.googlesource.com/external/webrtc.git/+/82ebe02491d066697717ae386f886b752729e013

commit 82ebe02491d066697717ae386f886b752729e013
Author: hbos <hbos@webrtc.org>
Date: Mon Nov 14 09:41:09 2016

Correct stats for RTCPeerConnectionStats.dataChannels[Opened/Closed].

DataChannel.SignalOpened and unittests added.
PeerConnection.SignalDataChannelCreated added and wired up to
RTCStatsCollector.OnDataChannelCreated on RTCStatsCollector
construction.
RTCStatsCollector.OnSignalOpened/Closed added and wired up on
OnDataChannelCreated.
rtcstatscollector_unittest.cc updated, faking that channels are opened
and closed.

I did not want to use DataChannelObserver because it is used for more
than state changes and there can only be one observer (unless code is
updated). Since DataChannel already had a SignalClosed it made sense to
add a SignalOpened.

Having OnSignalBlah in RTCStatsCollector is new in this CL but will
likely be needed to correctly handle RTPMediaStreamTracks being added
and detached independently of getStats. This CL establishes this
pattern.

(An integration test will be needed for this and all the other stats to
make sure everything is wired up correctly and test outside of a
mock/fake environment, but this is not news.)

BUG= chromium:636818 ,  chromium:627816 

Review-Url: https://codereview.webrtc.org/2472113002
Cr-Commit-Position: refs/heads/master@{#15059}

[modify] https://crrev.com/82ebe02491d066697717ae386f886b752729e013/webrtc/api/datachannel.cc
[modify] https://crrev.com/82ebe02491d066697717ae386f886b752729e013/webrtc/api/datachannel.h
[modify] https://crrev.com/82ebe02491d066697717ae386f886b752729e013/webrtc/api/datachannel_unittest.cc
[modify] https://crrev.com/82ebe02491d066697717ae386f886b752729e013/webrtc/api/peerconnection.cc
[modify] https://crrev.com/82ebe02491d066697717ae386f886b752729e013/webrtc/api/peerconnection.h
[modify] https://crrev.com/82ebe02491d066697717ae386f886b752729e013/webrtc/api/rtcstatscollector.cc
[modify] https://crrev.com/82ebe02491d066697717ae386f886b752729e013/webrtc/api/rtcstatscollector.h
[modify] https://crrev.com/82ebe02491d066697717ae386f886b752729e013/webrtc/api/rtcstatscollector_unittest.cc

[bulk-edit : please ignore if not applicable]

Could you please set the correct milestone for this issue?

The following revision refers to this bug:
  https://chromium.googlesource.com/external/webrtc.git/+/42eee12614c8b931f416c9830dc247eba85e73b1

commit 42eee12614c8b931f416c9830dc247eba85e73b1
Author: hbos <hbos@webrtc.org>
Date: Wed Nov 23 15:43:23 2016

RTCPeerConnectionStats: Removed fixed TODO comments.

I forget to remove these when fixing them.

BUG= chromium:636818 
NOTRY=True
NOPRESUBMIT=True

Review-Url: https://codereview.webrtc.org/2522023003
Cr-Commit-Position: refs/heads/master@{#15215}

[modify] https://crrev.com/42eee12614c8b931f416c9830dc247eba85e73b1/webrtc/api/stats/rtcstats_objects.h

The following revision refers to this bug:
  https://chromium.googlesource.com/external/webrtc.git/+/42eee12614c8b931f416c9830dc247eba85e73b1

commit 42eee12614c8b931f416c9830dc247eba85e73b1
Author: hbos <hbos@webrtc.org>
Date: Wed Nov 23 15:43:23 2016

RTCPeerConnectionStats: Removed fixed TODO comments.

I forget to remove these when fixing them.

BUG= chromium:636818 
NOTRY=True
NOPRESUBMIT=True

Review-Url: https://codereview.webrtc.org/2522023003
Cr-Commit-Position: refs/heads/master@{#15215}

[modify] https://crrev.com/42eee12614c8b931f416c9830dc247eba85e73b1/webrtc/api/stats/rtcstats_objects.h