chromeos: turn on simplified display management for mash

I'm going to keep the function to determine if enabled. Assuming there
aren't any issues after a couple of days I'll do a cleanup pass.

BUG=718860
TEST=none
R=msw@chromium.org

Review-Url: https://codereview.chromium.org/2906873003
Cr-Commit-Position: refs/heads/master@{#477150}
14 files changed