The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d17b445e932a10c875cea034b037b19d30e47a8c

commit d17b445e932a10c875cea034b037b19d30e47a8c
Author: lawrencewu <lawrencewu@chromium.org>
Date: Tue Dec 13 19:54:32 2016

Share field trial allocator on Mac

This CL shares the field trial allocator on MacOS. It depends on Mac having
POSIX shared memory support, but other than that it is basically the same mechanism as that in the Linux CL: https://codereview.chromium.org/2530573002/. We basically just need to edit some ifdefs.

NOTE: turning on NOPRESUBMIT because the dependent CL re-adds some banned calls to AllowIO.

BUG= 663912 
NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/2565683003
Cr-Commit-Position: refs/heads/master@{#438265}

[modify] https://crrev.com/d17b445e932a10c875cea034b037b19d30e47a8c/base/memory/shared_memory_handle.h
[modify] https://crrev.com/d17b445e932a10c875cea034b037b19d30e47a8c/base/memory/shared_memory_handle_mac.cc
[modify] https://crrev.com/d17b445e932a10c875cea034b037b19d30e47a8c/base/metrics/field_trial.cc
[modify] https://crrev.com/d17b445e932a10c875cea034b037b19d30e47a8c/base/metrics/field_trial.h

Today's canary (57.0.2951.0) has the changes and looks like they're working as far as I can tell! I glanced at a sample crash report and it has the --field-trial-handle=1 flag and no old flags and has all the field trials visible in the crash report. Great! I also glanced at the crashes we have currently and didn't see anything related - so (cross fingers) looks like it's all working fine. :D

Awesome!! I'm super excited to see this land in stable!