GitLab

As a follow-up to crrev.com/c/2562778, moves all sign-in utilities to
the new signin namespace.

Bug: 1157531
Change-Id: Ic695832a7cd5778e69039b2d3fd1395de3cde50c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2593259Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Nohemi Fernandez <fernandex@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837501}