Data race fix: Replace use of MessageLoop raw pointer in MSAudioProcessor.

Data race fix: Replace use of MessageLoop raw pointer in MSAudioProcessor.

This change replaces the use of a raw pointer to the main thread's
MessageLoop, by content::MediaStreamAudioProcessor, with a
scoped_refptr to the main thread's task runner. This fixes a
TSan-reported shutdown data race which was caused by the MessageLoop
releasing its task runner at the same time the audio thread was using
the MessageLoop::task_runner() accessor method.

BUG=647178
Committed: https://crrev.com/a4717b9caba5b1fb1e4455af8932a3a870a9aecf
Cr-Commit-Position: refs/heads/master@{#426318}

[miu, 2016-10-19 02:06:39]

miu@chromium.org changed reviewers:
+ perkj@chromium.org

[miu, 2016-10-19 02:06:40]

perkj: PTAL.

https://chromiumcodereview.appspot.com/2425353002/diff/1/content/renderer/med...
File content/renderer/media/media_stream_audio_processor.cc (right):

https://chromiumcodereview.appspot.com/2425353002/diff/1/content/renderer/med...
content/renderer/media/media_stream_audio_processor.cc:815:
main_thread_runner_->PostTask(
Note: This LOC is where the data race occurred.

[perkj_chrome, 2016-10-19 03:21:29]

lgtm

[miu, 2016-10-19 03:35:26]

The CQ bit was checked by miu@chromium.org

[commit-bot: I haz the power, 2016-10-19 03:37:33]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-19 05:28:29]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-10-19 05:28:30]

Try jobs failed on following builders:
  mac_chromium_rel_ng on master.tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[miu, 2016-10-19 21:28:42]

On 2016/10/19 05:28:30, commit-bot: I haz the power wrote:
> Try jobs failed on following builders:
>   mac_chromium_rel_ng on master.tryserver.chromium.mac (JOB_FAILED,
>
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

Whoops! I ran the browser tests, but forget to run content_unittests. Looks like
the tests need to instantiate a task runner for the main thread.

[miu, 2016-10-19 21:29:17]

The CQ bit was checked by miu@chromium.org

[miu, 2016-10-19 21:29:17]

The patchset sent to the CQ was uploaded after l-g-t-m from perkj@chromium.org
Link to the patchset: https://codereview.chromium.org/2425353002/#ps20001
(title: "Fix unit tests: They all need a MessageLoop instantiated.")

[commit-bot: I haz the power, 2016-10-19 21:30:04]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-10-19 23:05:19]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-10-21 13:12:43]

Description was changed from

==========
Data race fix: Replace use of MessageLoop raw pointer in MSAudioProcessor.

This change replaces the use of a raw pointer to the main thread's
MessageLoop, by content::MediaStreamAudioProcessor, with a
scoped_refptr to the main thread's task runner. This fixes a
TSan-reported shutdown data race which was caused by the MessageLoop
releasing its task runner at the same time the audio thread was using
the MessageLoop::task_runner() accessor method.

BUG=647178
==========

to

==========
Data race fix: Replace use of MessageLoop raw pointer in MSAudioProcessor.

This change replaces the use of a raw pointer to the main thread's
MessageLoop, by content::MediaStreamAudioProcessor, with a
scoped_refptr to the main thread's task runner. This fixes a
TSan-reported shutdown data race which was caused by the MessageLoop
releasing its task runner at the same time the audio thread was using
the MessageLoop::task_runner() accessor method.

BUG=647178

Committed: https://crrev.com/a4717b9caba5b1fb1e4455af8932a3a870a9aecf
Cr-Commit-Position: refs/heads/master@{#426318}
==========

[commit-bot: I haz the power, 2016-10-21 13:12:43]

Patchset 2 (id:??) landed as
https://crrev.com/a4717b9caba5b1fb1e4455af8932a3a870a9aecf
Cr-Commit-Position: refs/heads/master@{#426318}