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This preview status will be copied into the DRP pingback. This CL is
factored out for sake of timing WRT branch later today.

This CL also adds basic control-group variations support since that is
an important part of the preview status in the pingback.

Bug: 864665
Change-Id: Ib8ee672e4247da42b97015b89e85240122bc696e
Reviewed-on: https://chromium-review.googlesource.com/c/1355550Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Commit-Queue: Robert Ogden <robertogden@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612572}