printing: wait for primary profile in CupsProxyServiceManager

CupsProxyServiceManager spawns CupsProxyService, which depends on the
primary profile existing. Before spawning CupsProxyService, check to
make sure the primary profile exists. If the primary profile does not
exist, CupsProxyServiceManager will continue periodically checking for
the primary profile's existence until it reaches an attempt limit, when
it will then stop trying to spawn CupsProxyService.

Bug: crbug:1424583
Change-Id: I4baecf0387fb066175e7e55c9ae598503293bdd1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4401076
Reviewed-by: Benjamin Gordon <bmgordon@chromium.org>
Commit-Queue: Paul Moy <pmoy@chromium.org>
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1144186}