GitLab

Keep the picker disabled on startup until:
- multiple profiles were used in the last 28 days, or
- the picker has been shown once

A new prefs::kBrowserProfilePickerShown pref is added to track whether
the picker has been shown before.

Bug: 1063856
Change-Id: Ia35a3b2212b3811ed592d81fa516bc1ffc07accc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2598848
Commit-Queue: Alex Ilin <alexilin@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840598}