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* Disable network configuration field if the field is enforced by policy.
* Add policy network indicator if the field is controlled by policy.

Bug: 877424
Change-Id: Icfdb6d7fb3deb09696b6d2edce27d3c9851043a2
Reviewed-on: https://chromium-review.googlesource.com/c/1251447
Commit-Queue: Nikita Podguzov <nikitapodguzov@google.com>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Alexander Hendrich <hendrich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600735}