Add 'Managed UI' on chrome://settings

Adds a message for managed users at the top of the chrome://settings
page.

Enterprise users will now see a message that says "Your browser is
managed by your organization", with a link they can click to view a help
center article.

The new UI is hidden behind a flag so that most users don't see this WIP
feature just yet.

Bug: 893628
Change-Id: I878497a5f39cb2a86015af5331198bfffbcf53a3
Reviewed-on: https://chromium-review.googlesource.com/c/1401509
Commit-Queue: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Reviewed-by: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624649}
5 files changed