17c87d05da
This creates a new service that stores precisely two bits per RP, IDP, and account ID tuple: has it been used before and is it able to be logged out. It does so with the additional constraints of respecting private browsing's clear on last session and in-memory storage constraints and being a participant in the Clear Storage Service. Tests are here. Coverage isn't perfect, but they cover most of the service. Differential Revision: https://phabricator.services.mozilla.com/D162124