[Managed Session] Force managed sessions mode when network certificates are set via ONC device policy

The same way as force-installed extensions, forced network certificates are considered "risky" should activate "Managed Session" mode (i.e. show warning about admin capabilities on the login page).

Bug: 910218
Change-Id: Ic34898ed255f51b48b948b00ae4563bcd7939347
Reviewed-on: https://chromium-review.googlesource.com/c/1391590
Commit-Queue: Zakhar Voit <voit@google.com>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625174}
2 files changed