GitLab

This commit grays out unmanaged WiFis and button to joining other WiFis
when AllowOnlyPolicyNetworksToConnect is true after user logged in, as
well as adds the tooltip to tell users why.

BUG=208378

Review URL: https://codereview.chromium.org/1469733003

Cr-Commit-Position: refs/heads/master@{#361319}