hta@, could you PTAL?

This is currently below the rader of try-flakes, so it doesn't yet appear on sheriff-o-matic, but it is probably something worth looking into.

Actually, this test has been consistently failing in the last 3 runs of https://uberchromegw.corp.google.com/i/chromium.mac/builders/Mac10.9%20Tests%20%28dbg%29

Because of the above (and because hta@ is in another timezone so I can't ping him on chat for his opinion), maybe I'll just go ahead and disable this test.

I have a WIP CL to disable the test on Mac at https://crrev.com/2799663006

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e0f62aa119e65f04322c7d51b09c7e75dc2adc53

commit e0f62aa119e65f04322c7d51b09c7e75dc2adc53
Author: lukasza <lukasza@chromium.org>
Date: Fri Apr 07 00:15:20 2017

Disable MediaStreamAudioTest.CallbackOnTrackInitialization on Mac.

Disabling the test, because it has been consistently failing
for the last 3 builds on Mac10.9 Tests (dbg).  OTOH, note that
FindIt says that it cannot find the culprit CL and thinks that
the test is just flaky.  In either case, disabling the test seems like
the right thing to do.

BUG= 709231 
TBR=hta@chromium.org

Review-Url: https://codereview.chromium.org/2799663006
Cr-Commit-Position: refs/heads/master@{#462701}

[modify] https://crrev.com/e0f62aa119e65f04322c7d51b09c7e75dc2adc53/content/renderer/media/media_stream_audio_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/2c6775c0307883f2c1cd1abdc1b9eaa7a2897164

commit 2c6775c0307883f2c1cd1abdc1b9eaa7a2897164
Author: foolip <foolip@chromium.org>
Date: Fri Apr 07 06:34:43 2017

Revert of Disable MediaStreamAudioTest.CallbackOnTrackInitialization on Mac. (patchset #1 id:1 of https://codereview.chromium.org/2799663006/ )

Reason for revert:
Whole test should be reverted:
https://codereview.chromium.org/2803183002/

Original issue's description:
> Disable MediaStreamAudioTest.CallbackOnTrackInitialization on Mac.
>
> Disabling the test, because it has been consistently failing
> for the last 3 builds on Mac10.9 Tests (dbg).  OTOH, note that
> FindIt says that it cannot find the culprit CL and thinks that
> the test is just flaky.  In either case, disabling the test seems like
> the right thing to do.
>
> BUG= 709231 
> TBR=hta@chromium.org
>
> Review-Url: https://codereview.chromium.org/2799663006
> Cr-Commit-Position: refs/heads/master@{#462701}
> Committed: https://chromium.googlesource.com/chromium/src/+/e0f62aa119e65f04322c7d51b09c7e75dc2adc53

TBR=hta@chromium.org,lukasza@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG= 709231 

Review-Url: https://codereview.chromium.org/2805443004
Cr-Commit-Position: refs/heads/master@{#462793}

[modify] https://crrev.com/2c6775c0307883f2c1cd1abdc1b9eaa7a2897164/content/renderer/media/media_stream_audio_unittest.cc

 Issue 709497  has been merged into this issue.

This issue should be taken care of by reverting the CL that caused the test failures - the revert is in r462797.

Findit identified the culprit that introduced the flakiness as https://codereview.chromium.org/2777583002 based on analysis https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyswELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCJ9Y2hyb21pdW0ubWFjL01hYzEwLjkgVGVzdHMgKGRiZykvMzg5OTMvY29udGVudF91bml0dGVzdHMvVFdWa2FXRlRkSEpsWVcxQmRXUnBiMVJsYzNRdVEyRnNiR0poWTJ0UGJsUnlZV05yU1c1cGRHbGhiR2w2WVhScGIyND0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA