Fix base::internal::Singleton to use acquire loads instead of nobarrier ones.

Fix base::internal::Singleton to use acquire loads instead of nobarrier ones.
The NoBarrier_Load operations don't actually guarantee that the singleton data
associated with the pointer is visible to the thread calling get() even if the
pointer is initialized.

R=mark@chromium.org, dvyukov@chromium.org, epenner@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=255552

[Alexander Potapenko, 2014-03-06 12:41:46]

Please take a look.

[Mark Mentovai, 2014-03-06 14:28:59]

LGTM

[Dmitry Vyukov, 2014-03-06 14:36:28]

LGTM

[Alexander Potapenko, 2014-03-07 05:22:47]

The CQ bit was checked by glider@chromium.org

[commit-bot: I haz the power, 2014-03-07 05:24:05]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/glider@chromium.org/188603002/1

[commit-bot: I haz the power, 2014-03-07 05:54:27]

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

[commit-bot: I haz the power, 2014-03-07 05:54:27]

Retried try job too often on chromium_presubmit for step(s) presubmit
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=chromium_p...

[Alexander Potapenko, 2014-03-07 07:03:38]

The CQ bit was checked by glider@chromium.org

[commit-bot: I haz the power, 2014-03-07 07:05:26]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/glider@chromium.org/188603002/1

[commit-bot: I haz the power, 2014-03-07 07:26:15]

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

[commit-bot: I haz the power, 2014-03-07 07:26:15]

Retried try job too often on chromium_presubmit for step(s) presubmit
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=chromium_p...

[Alexander Potapenko, 2014-03-07 08:51:48]

Committed patchset #1 manually as r255552.