Seen here:
https://luci-milo.appspot.com/buildbot/tryserver.chromium.win/win_chromium_rel_ng/515758

Failure log:
[ RUN      ] WebRtcMediaRecorderTest.TwoChannelAudioRecording
DevTools listening on ws://127.0.0.1:61233/devtools/browser/f46aed2e-0016-486e-9aa0-d426230b6e07
[5076:4648:0818/160822.786:27819190:ERROR:direct_composition_surface_win.cc(1095)] Failing to detect HDR, couldn't retrieve D3D11 device from ANGLE.
[5076:4648:0818/160822.790:27819190:INFO:media_foundation_video_encode_accelerator_win.cc(335)] Windows versions earlier than 8 are not supported.
[6020:2392:0818/160823.397:27819798:INFO:CONSOLE(104)] "Recorder object created.", source: http://127.0.0.1:61234/media/mediarecorder_test.html (104)
[6020:2392:0818/160823.400:27819798:INFO:CONSOLE(22)] "Waiting for", source: http://127.0.0.1:61234/media/mediarecorder_test_utils.js (22)
From javascript: Error: timecodes
    at failTest (http://127.0.0.1:61234/media/webrtc_test_utilities.js:42:15)
    at assertTrue (http://127.0.0.1:61234/media/webrtc_test_utilities.js:278:5)
    at MediaRecorder.recorder.ondataavailable (http://127.0.0.1:61234/media/mediarecorder_test.html:519:13)
When executing 'testTwoChannelAudio();'
../../content/browser/webrtc/webrtc_content_browsertest_base.cc(91): error: Failed
[  FAILED  ] WebRtcMediaRecorderTest.TwoChannelAudioRecording, where TypeParam =  and GetParam() =  (780 ms)


Only saw once instance of this on the tryserver. Please take a look.