Avoid deadlock during trace_event flush

Avoid deadlock during trace_event flush

The deadlock occurs because we hold lock when posting flush tasks.
If MessageLoop::PostTask() also calls TRACE_EVENT and the TRACE_EVENT
has never been reached before, the TRACE_EVENT will try to get the
category enabled flag which will also need a lock.

Copy thread_message_loops into a temporary vector of
scoped_refptr<SingleProcessTaskRunner> to avoid lock when calling
PostTask().

BUG=397022
TEST=Existing tests and ThreadSanitizer

Committed: https://crrev.com/bb113630cf9e1290eb211e8f9413f9dc4d4c5aab
Cr-Commit-Position: refs/heads/master@{#293144}

[Xianzhu, 2014-08-21 17:56:32]

dsinclair@ is on vacation. nduca@ could you ptal?

[Xianzhu, 2014-08-26 15:35:38]

ping...

[Xianzhu, 2014-08-28 01:40:52]

wangxianzhu@chromium.org changed reviewers:
+ dsinclair@chromium.org

[dsinclair, 2014-09-02 14:26:04]

lgtm

[Xianzhu, 2014-09-02 16:06:28]

The CQ bit was checked by wangxianzhu@chromium.org

[commit-bot: I haz the power, 2014-09-02 16:07:44]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/491393002/1

[commit-bot: I haz the power, 2014-09-02 16:18:28]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu/builds/...)
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/49073)
  win_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu/builds/54395)
  android_aosp on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_aosp/bu...)
  android_arm64_dbg_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_arm64_d...)
  android_chromium_gn_compile_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_chromiu...)
  android_clang_dbg_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)
  android_dbg_tests_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg_tes...)
  chromium_presubmit on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)
  linux_chromium_chromeos_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  linux_chromium_gn_rel on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  linux_chromium_rel_swarming on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)
  ios_rel_device on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device/bu...)
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)
  mac_chromium_compile_dbg on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)
  mac_chromium_rel_swarming on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)
  win8_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)
  win_chromium_compile_dbg on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_comp...)
  win_chromium_rel_swarming on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)
  win_chromium_x64_rel_swarming on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[commit-bot: I haz the power, 2014-09-02 16:20:37]

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

[commit-bot: I haz the power, 2014-09-02 16:20:38]

Try jobs failed on following builders:
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)

[Xianzhu, 2014-09-02 16:41:34]

The CQ bit was checked by wangxianzhu@chromium.org

[commit-bot: I haz the power, 2014-09-02 16:43:28]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/491393002/20001

[commit-bot: I haz the power, 2014-09-02 17:41:47]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  android_dbg_tests_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg_tes...)

[commit-bot: I haz the power, 2014-09-02 18:42:28]

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

[commit-bot: I haz the power, 2014-09-02 18:42:30]

Try jobs failed on following builders:
  android_dbg_tests_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_dbg_tes...)

[Xianzhu, 2014-09-02 22:45:42]

Unfortunately Patch Set 2 didn't work properly. The shared thread_message_loops
still needs lock to access. Patch Set 3 uses a simpler method that copies
thread_message_loops to a temporary vector of
scoped_refptr<SingleThreadTaskRunner> to avoid locks when calling PostTask().

PTAL.

[dsinclair, 2014-09-03 13:21:49]

lgtm

[Xianzhu, 2014-09-03 15:19:08]

The CQ bit was checked by wangxianzhu@chromium.org

[commit-bot: I haz the power, 2014-09-03 15:19:39]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/491393002/40001

[commit-bot: I haz the power, 2014-09-03 16:14:43]

Committed patchset #3 (id:40001) as ede32d2bfa75f6c02373dffb58582be7eb0aa7f9

[commit-bot: I haz the power, 2014-09-10 03:25:59]

Patchset 3 (id:??) landed as
https://crrev.com/bb113630cf9e1290eb211e8f9413f9dc4d4c5aab
Cr-Commit-Position: refs/heads/master@{#293144}