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This adds tests to verify that opt outs are actually recorded and
tracked appropriately for Previews.

Bug: 900724,778793
Change-Id: Ib927645256eeeb7df08092eeb80f5652f295edbc
Reviewed-on: https://chromium-review.googlesource.com/c/1311375
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604643}