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Adding an API that will refresh (refetch) Enterprise Policies when called.
This will remove the need for automated testing to go to the
chrome://policy page, and "click" the refresh button via a js call.

Bug=chromium:1012712
Test=Locally deployed and tested and basic unittest.

Change-Id: Iedc3c2e349cceb7f8b076259877d548b9f4babda
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1683103
Commit-Queue: Derek Beckett <dbeckett@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Achuith Bhandarkar <achuith@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707382}