Add policy to control scheduler configuration.

This exposes the already existing kSchedulerConfiguration preference
to be controllable via an enterprise policy. The policy is per-user,
but not per-profile, i.e. we'll follow the configuration for the user
who logs into the device.

BUG=chromium:927840
TEST=Manual

Change-Id: I0f0c45d5ac6d3c9a289d7ec156af95800e221f7e
Reviewed-on: https://chromium-review.googlesource.com/c/1456068
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Lutz Justen <ljusten@chromium.org>
Commit-Queue: Mattias Nissler <mnissler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631829}
4 files changed