Whitelist intentionally racy TRACE_EVENT reads and writes.

Whitelist intentionally racy TRACE_EVENT reads and writes.

Chrome's tracing framework appears to be intentionally racy on its
quick-reject checks, trading some data loss for better performance
when disabled.  People will never notice the data loss, but TSAN does.
Let's assuage TSAN with some annotations.

The 'volatile' val in SK_ANNOTATE_UNPROTECTED_WRITE was making this
not compile, but that volatile doesn't really make sense there: the value we're
writing is not what we care about, it's the destination.

CQ_EXTRA_TRYBOTS=client.skia:Test-Ubuntu13.10-GCE-NoGPU-x86_64-Release-TSAN-Trybot

No API changes.
TBR=reed

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/e974c6244c92d32a0e4fe5639a913e78f101a056

[mtklein, 2014-11-05 15:09:26]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-11-05 15:09:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/702883002/1

[commit-bot: I haz the power, 2014-11-05 15:09:45]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2014-11-05 21:09 UTC

[commit-bot: I haz the power, 2014-11-05 15:17:46]

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

[commit-bot: I haz the power, 2014-11-05 15:17:47]

Try jobs failed on following builders:
  Test-Ubuntu13.10-GCE-NoGPU-x86_64-Release-TSAN-Trybot on client.skia
(http://build.chromium.org/p/client.skia/builders/Test-Ubuntu13.10-GCE-NoGPU-x...)

[mtklein, 2014-11-05 15:25:32]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-11-05 15:25:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/702883002/20001

[commit-bot: I haz the power, 2014-11-05 15:25:45]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2014-11-05 21:25 UTC

[commit-bot: I haz the power, 2014-11-05 15:25:48]

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

[commit-bot: I haz the power, 2014-11-05 15:25:48]

Presubmit check for 702883002-20001 failed and returned exit status 1.

Running presubmit commit checks ...

** Presubmit ERRORS **
Since the CL is editing public API, you must have an LGTM from one of:
('reed@chromium.org', 'reed@google.com', 'bsalomon@chromium.org',
'bsalomon@google.com', 'djsollen@chromium.org', 'djsollen@google.com')

[mtklein, 2014-11-05 15:27:28]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-11-05 15:27:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/702883002/20001

[mtklein, 2014-11-05 15:28:12]

The CQ bit was unchecked by mtklein@google.com

[mtklein, 2014-11-05 15:55:06]

mtklein@google.com changed reviewers:
+ bungeman@google.com

[bungeman-skia, 2014-11-05 16:01:27]

lgtm

[mtklein, 2014-11-05 16:02:07]

The CQ bit was unchecked by mtklein@google.com

[mtklein, 2014-11-05 16:02:08]

The CQ bit was checked by mtklein@google.com

[mtklein, 2014-11-05 16:02:09]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-11-05 16:03:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/702883002/20001

[commit-bot: I haz the power, 2014-11-05 16:03:33]

Committed patchset #2 (id:20001) as e974c6244c92d32a0e4fe5639a913e78f101a056