Add policy checks to SmbShare UI.

If the policy for NetworkFileSharesAllowed is set to false, users will
not be able to mount shares nor will the be able to access the mount ui


Bug: chromium:757625
Change-Id: Ief64c9a9c3c2a574b931bc3f21516d471c26bcd4
Reviewed-on: https://chromium-review.googlesource.com/1152490
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584443}
5 files changed