Will wait until branch point to land.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f8d5915aabda618649aea2495a8b08da938cb269

commit f8d5915aabda618649aea2495a8b08da938cb269
Author: asvitkine <asvitkine@chromium.org>
Date: Mon Jan 23 20:14:09 2017

Enable field trial shared memory segment on Android.

This is the last platform (not counting iOS) that didn't have this support,
which was added last fall for the other platforms. The other platforms
were enabled under crbug.com/663918

Turns out, it just works.

I tested this on a local build and verified that things are working correctly
via an induced chrome://crash which had all the field trials and the expected
command line flags.

This CL mostly cleans up the ifdefs and moves one function so that its order
matches the header file. Also reduces the !NACL ifdefs by defining an anon
wrapper around TerminateBecauseOutOfMemory() which doesn't exist for
NACL.

BUG= 681695 

Review-Url: https://codereview.chromium.org/2633203002
Cr-Commit-Position: refs/heads/master@{#445457}

[modify] https://crrev.com/f8d5915aabda618649aea2495a8b08da938cb269/base/metrics/field_trial.cc
[modify] https://crrev.com/f8d5915aabda618649aea2495a8b08da938cb269/base/metrics/field_trial.h