The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/67b3fb402415a5e207f9c5bfe8b3d5d694066adc

commit 67b3fb402415a5e207f9c5bfe8b3d5d694066adc
Author: Tommy Steimel <steimel@chromium.org>
Date: Wed Nov 15 18:23:42 2017

Add UKM for site muting

This CL logs UKM events when a site tries to play sound and is blocked.
The event also track the reason for muting (either because the sound
setting is BLOCK by default, or because the user has added an explicit
BLOCK exception for the given site).

Bug:  777911 
Change-Id: Ifc507ac6ddf31a37e5b61b3766ca830383232f9a
Reviewed-on: https://chromium-review.googlesource.com/760663
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516750}
[modify] https://crrev.com/67b3fb402415a5e207f9c5bfe8b3d5d694066adc/chrome/browser/android/tab_web_contents_delegate_android.cc
[modify] https://crrev.com/67b3fb402415a5e207f9c5bfe8b3d5d694066adc/chrome/browser/android/tab_web_contents_delegate_android.h
[modify] https://crrev.com/67b3fb402415a5e207f9c5bfe8b3d5d694066adc/chrome/browser/content_settings/sound_content_setting_observer.cc
[modify] https://crrev.com/67b3fb402415a5e207f9c5bfe8b3d5d694066adc/chrome/browser/content_settings/sound_content_setting_observer.h
[modify] https://crrev.com/67b3fb402415a5e207f9c5bfe8b3d5d694066adc/chrome/browser/content_settings/sound_content_setting_observer_unittest.cc
[modify] https://crrev.com/67b3fb402415a5e207f9c5bfe8b3d5d694066adc/chrome/browser/content_settings/tab_specific_content_settings.cc
[modify] https://crrev.com/67b3fb402415a5e207f9c5bfe8b3d5d694066adc/chrome/browser/content_settings/tab_specific_content_settings.h
[modify] https://crrev.com/67b3fb402415a5e207f9c5bfe8b3d5d694066adc/chrome/browser/content_settings/tab_specific_content_settings_unittest.cc
[modify] https://crrev.com/67b3fb402415a5e207f9c5bfe8b3d5d694066adc/chrome/browser/ui/browser.cc
[modify] https://crrev.com/67b3fb402415a5e207f9c5bfe8b3d5d694066adc/tools/metrics/ukm/ukm.xml