Autoplay: Force enable on desktop for Web Audio

Force enable on desktop for Web Audio.

BUG=841933

Change-Id: I29a5257973c777c84c046576518e970d7cb0d2ba
Reviewed-on: https://chromium-review.googlesource.com/1054433
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#557945}
Cr-Commit-Position: refs/branch-heads/3359@{#827}
Cr-Branched-From: 66afc5e5d10127546cc4b98b9117aff588b5e66b-refs/heads/master@{#540276}
7 files changed