GitLab

Move away from SigninManager[Base] in favor of the IdentityManager
for every single API call except for OnExternalSigninCompleted(),
which hasn't got mapped yet to the IdentityManager (crbug.com/889902).

Bug: 882464
Change-Id: I68c8b4845caaed59dd9b2650da977fac74be06b4
Reviewed-on: https://chromium-review.googlesource.com/c/1333390
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608059}