GitLab

- drop LoginDisplayHost::default_host(), we're already in the default_host()
  instance
- remove early-return
- check if we're currently signing in, in which case do not show gaia (fixes the
  bug)

Bug: 852745
Change-Id: I5e1e7dcfca2c7aca55b9301721ea3499c1a88451
Reviewed-on: https://chromium-review.googlesource.com/1110273Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569771}