GitLab

This CL hooks ozone/wayland with the newly added 'layout_mode'
event, from zaura_shell EXO extension.

It also introduces a new path to set the global tablet state:
display::DisplayObserver.

Next, ash/wm/tablet_mode/tablet_more_controller.cc|h will switch
over to it, and rest chromeos::TabletState.

BUG=1113900

R=jamescook@chromium.org, rjkroege@chromium.org

Change-Id: Iae832c4247c04c47429255721ff69c3ba0762455
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2491517Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Robert Kroeger <rjkroege@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#823948}