Add policy for NetBios SMB Share discovery

This change adds an enterprise policy that disables NetBios share discovery
by default for enterprises and allows enterprises to manually turn it on.
NetBios discovery will be on for non-enterprise users.

This change does include any code to enforce the policy.

Bug: chromium:757625
Change-Id: I30288a13ef89378f021364b6f1fe4cead4e44afe
Reviewed-on: https://chromium-review.googlesource.com/1184240
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585345}
7 files changed