Explicitly pass a callback when loading attachments.

This is part of moving away from the explicit setCallback,
which either has race conditions or is very noisy, or both.
(Each IEmailService call that wants callbacks should just
pass the callback explicitly.)

I'm not yet changing how the services actually handle the
call. Each protocol will need to fix this on their own.

Bug: 9735207
Bug: 9842867
Change-Id: If8cf69ffe82f3544ace9e58b1db5a183f38d038a
6 files changed