Port 28190980

Original Commit Message:

    This patch also moves Shell::Exit to base::OS::ExitProcess.

R=ulan@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: I0a7dc051ed5a21ad9641d1d05182ea4240bc666a
Reviewed-on: https://chromium-review.googlesource.com/976332Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#52164}