Make ProfileSyncService::IsFirstSetupComplete private and non-virtual

SyncUserSettings::IsFirstSetupComplete is the new way to check this.
This also switches the last few call sites of PSS::IFSC over to the new
way.

Bug: 884159
Change-Id: Ie3cf1ac36aee82b1f728c604ad86a381f9d78df0
Reviewed-on: https://chromium-review.googlesource.com/c/1382449
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Mohamed Amir Yosef <mamir@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Reviewed-by: Yury Khmel <khmel@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621103}
10 files changed