The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/20fce7f0c871dfade3228408e8aa3663031f51d6

commit 20fce7f0c871dfade3228408e8aa3663031f51d6
Author: Mounir Lamouri <mlamouri@chromium.org>
Date: Thu Feb 08 21:24:08 2018

Autoplay: add warning message when detecting usage of gesture=media.

This is also adding a UseCounter. The attribute is only caught at
parsing in order to avoid feature detection and is otherwise a no-op.

An custom message is used over a `Deprecation` warning to avoid any
kind of confusion around the feature "working but being deprecated".

Bug:  807610 
Change-Id: Ic06e76d1180f42cd1295f8874713122d066be95f
Reviewed-on: https://chromium-review.googlesource.com/895537
Reviewed-by: Rick Byers <rbyers@chromium.org>
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#535515}
[add] https://crrev.com/20fce7f0c871dfade3228408e8aa3663031f51d6/third_party/WebKit/LayoutTests/media/autoplay/console-warning-gesture-media-expected.txt
[add] https://crrev.com/20fce7f0c871dfade3228408e8aa3663031f51d6/third_party/WebKit/LayoutTests/media/autoplay/console-warning-gesture-media.html
[modify] https://crrev.com/20fce7f0c871dfade3228408e8aa3663031f51d6/third_party/WebKit/Source/core/html/HTMLIFrameElement.cpp
[modify] https://crrev.com/20fce7f0c871dfade3228408e8aa3663031f51d6/third_party/WebKit/public/platform/web_feature.mojom
[modify] https://crrev.com/20fce7f0c871dfade3228408e8aa3663031f51d6/tools/metrics/histograms/enums.xml