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This is using the UKM service to record the autoplay attempts and
the unmute results.

Bug: 744659
Change-Id: Ice9a259a4006beff1044e5ed62981619841895e5
Reviewed-on: https://chromium-review.googlesource.com/525692
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Chris Palmer <palmer@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#509384}