[signin] Fix account consistency value on the IO thread

The account consistency was wrong on the IO thread: it was rebuilt
from the Finch experiment config and the migration pref. However
this is not enough, and edge cases were missed, such as supervised
profiles and missing client ID.

This CL no longer rebuilds the account consistency method on the IO
thread, but instead simply passes the value from the UI thread.

Bug: 844250
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_mojo
Change-Id: I735005277823196a31553cc85010ca0c89eed30b
Reviewed-on: https://chromium-review.googlesource.com/1097403
Commit-Queue: David Roger <droger@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#566832}
11 files changed