UMA for result of lock_to_single_user DBus call.

If the policy dictates to lock the device to single user, the failure
to do so generates the user to be logged out. Here we add UMA stats to
have metrics on how often this happens.

BUG=b:77799573
TEST=None

Change-Id: I5eea6616628c2130f25c746b3ce9cabd63d139a9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1595868
Commit-Queue: Igor <igorcov@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Igor <igorcov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659955}
3 files changed