The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8095c757053bd2bc15b5b2570362587ba38c5779

commit 8095c757053bd2bc15b5b2570362587ba38c5779
Author: asvitkine <asvitkine@chromium.org>
Date: Tue Dec 13 18:37:55 2016

NoBarrier_Load()/NoBarrier_Store() for manipulating activated field.

These ops guarantee atomicity of the write/read (i.e. not partial), but
do not put constraints around synchronization and ordering.

This is mostly academic since the field's value is either 0 or 1, so
currently is not susceptible to issues from partial writes of the
data.

It does not need synchronization or ordering constraints because it's
ok for child processes to observe a stale value because it's only used
to avoid sending a no-op IPC to browser process if child knows trial is
activated. Still, this came up during design review and it doesn't hurt
to use these.

BUG= 673042 

Review-Url: https://codereview.chromium.org/2570473003
Cr-Commit-Position: refs/heads/master@{#438235}

[modify] https://crrev.com/8095c757053bd2bc15b5b2570362587ba38c5779/base/metrics/field_trial.cc
[modify] https://crrev.com/8095c757053bd2bc15b5b2570362587ba38c5779/base/metrics/field_trial.h