Currently nsAppRunner is responsible for choosing or creating a profile to use
at startup. It then has to create a reset profile if necessary and lock the
selected profile directories. But these latter things are done in different
places of the selection code and done in different ways, sometimes we delay
while trying to get the lock, sometimes we don't.
This patch moves the profile selection part of the code to its own function so
that then we only have to have one place that does the profile reset and
locking logic.
It makes a lot of sense to have the selection code live in the profile service.
It can use information from the database load to help make the choices and it
also means that we can expose the profile selection code through xpcom allowing
it to be easily automatically tested. It will also be more important for future
patches for the dedicated profiles feature.
Differential Revision: https://phabricator.services.mozilla.com/D16116
6e8218eb19