See http://crbug/859185 - a policy wasn't flagged as "can_be_recommended" but was being recommended in practise, and it was working. Only allowing "mandatory" broke existing uses, so this enforcement was reverted.

There are many other policies like this - every policy in kSimplePolicyMap can be
recommended in practise, regardless of whether it is documented as such. Either these policies
should not be able to be recommended, or documentation should be updated
so that it is clear that they can be recommended.

Documentation about the default values of "can_be_recommended" and "can_be_mandatory" should also be improved.