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As the experiment was successful we are now proceeding with the launch
of the overflow icons. This switches them on by default.

BUG=763301

Change-Id: If3f2cf5dc4537a7fa700c56775827ccb4cd4663d
Reviewed-on: https://chromium-review.googlesource.com/970342
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544713}