The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/14cb7c1e23e861b3c5be4602b818008ead6ff397

commit 14cb7c1e23e861b3c5be4602b818008ead6ff397
Author: Qiang Xu <warx@chromium.org>
Date: Wed Sep 06 02:09:35 2017

cros: move SuspendMediaSessions to ash::mojom::MediaClient

changes:
- SuspendMediaSessions used to live in ash::ShellDelegate to call into
chrome. This change moves SuspendMediaSessions to
ash::mojom::MediaClient.
- Add ash::TestMediaClient to support writing unittests

TabletPowerButtonControllerTest.SuspendMediaSessions

Test: tested on device and ash_unittests
Bug:  762111 
Change-Id: If97cbc8c051b46a4f46097c061742a09ece608a4
Reviewed-on: https://chromium-review.googlesource.com/651555
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Qiang(Joe) Xu <warx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#499849}
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/BUILD.gn
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/media_controller.cc
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/media_controller.h
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/public/interfaces/media.mojom
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/shell_delegate.h
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/system/power/power_button_display_controller.cc
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/system/power/tablet_power_button_controller_unittest.cc
[add] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/test_media_client.cc
[add] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/test_media_client.h
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/test_shell_delegate.cc
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/ash/test_shell_delegate.h
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/chrome/browser/ui/ash/chrome_shell_delegate.cc
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/chrome/browser/ui/ash/chrome_shell_delegate.h
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/chrome/browser/ui/ash/media_client.cc
[modify] https://crrev.com/14cb7c1e23e861b3c5be4602b818008ead6ff397/chrome/browser/ui/ash/media_client.h