FWIW, there is a ContentSettings.Exceptions.autoplay that records how many autoplay exceptions are set. We want to know about users disabling the feature (contrary to simply set exceptions). I'm not sure if there are common pattern in settings to deal with this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bd376092ad7bf6a2764f31eeee556f4b2c77584b

commit bd376092ad7bf6a2764f31eeee556f4b2c77584b
Author: finnur <finnur@chromium.org>
Date: Fri Jul 01 17:07:19 2016

Site Settings Android: Add UMA for measuring the Autoplay
default setting value at profile startup.

BUG= 622713 

Review-Url: https://codereview.chromium.org/2115873002
Cr-Commit-Position: refs/heads/master@{#403473}

[modify] https://crrev.com/bd376092ad7bf6a2764f31eeee556f4b2c77584b/components/content_settings/core/browser/content_settings_default_provider.cc
[modify] https://crrev.com/bd376092ad7bf6a2764f31eeee556f4b2c77584b/tools/metrics/histograms/histograms.xml

This needs to be merged to the M53 branch, which I understand was cut yesterday.

Your change meets the bar and is auto-approved for M53 (branch: 2785)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/59710b712a89a124805fe7725d57743569795aae

commit 59710b712a89a124805fe7725d57743569795aae
Author: Finnur Thorarinsson <finnur@chromium.org>
Date: Mon Jul 04 10:25:14 2016

Site Settings Android: Add UMA for measuring the Autoplay default setting value at profile startup.

BUG= 622713 

Review-Url: https://codereview.chromium.org/2115873002
Cr-Commit-Position: refs/heads/master@{#403473}
(cherry picked from commit bd376092ad7bf6a2764f31eeee556f4b2c77584b)

Review URL: https://codereview.chromium.org/2115423002 .

Cr-Commit-Position: refs/branch-heads/2785@{#10}
Cr-Branched-From: 68623971be0cfc492a2cb0427d7f478e7b214c24-refs/heads/master@{#403382}

[modify] https://crrev.com/59710b712a89a124805fe7725d57743569795aae/components/content_settings/core/browser/content_settings_default_provider.cc
[modify] https://crrev.com/59710b712a89a124805fe7725d57743569795aae/tools/metrics/histograms/histograms.xml

Thank you Finnur! :)