The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b9057f7dd59e9290e71a4985a1e709ea1a4365f5

commit b9057f7dd59e9290e71a4985a1e709ea1a4365f5
Author: Sammie Quon <sammiequon@google.com>
Date: Thu Jul 20 23:44:02 2017

cros: Introduce tablet mode observer.

Move all tablet mode related events from shell observer to a new tablet mode observer.

Test: all trybots especially ash tests
Bug:  743148 
Change-Id: Idbc601cbf59476c3928fa7ba63ef1dd58fb83893
Reviewed-on: https://chromium-review.googlesource.com/572053
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Jonathan Ross <jonross@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488485}
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/BUILD.gn
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/app_list/app_list_presenter_delegate.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/app_list/app_list_presenter_delegate.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/display/screen_orientation_controller_chromeos.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/display/screen_orientation_controller_chromeos.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/frame/header_view.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/frame/header_view.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/shell.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/shell.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/shell_observer.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/system/brightness/tray_brightness.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/system/keyboard_brightness/tray_keyboard_brightness.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/system/overview/overview_button_tray.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/system/overview/overview_button_tray.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/system/power/tablet_power_button_controller.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/system/power/tablet_power_button_controller.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/system/rotation/tray_rotation_lock.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/system/rotation/tray_rotation_lock.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/virtual_keyboard_controller.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/virtual_keyboard_controller.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/wm/tablet_mode/tablet_mode_controller.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/wm/tablet_mode/tablet_mode_controller.h
[add] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/ash/wm/tablet_mode/tablet_mode_observer.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/chrome/browser/ui/ash/launcher/arc_app_window_launcher_controller.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/chrome/browser/ui/ash/launcher/arc_app_window_launcher_controller.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/chrome/browser/ui/views/frame/browser_non_client_frame_view_ash.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/chrome/browser/ui/views/frame/browser_non_client_frame_view_ash.h
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/components/exo/wm_helper_ash.cc
[modify] https://crrev.com/b9057f7dd59e9290e71a4985a1e709ea1a4365f5/components/exo/wm_helper_ash.h