Views based shelf will be disabled in OOBE state for now.
Change to button visibility should be done when enabling. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/16abb43dd01897f007590b790fd3a19f209b392a

commit 16abb43dd01897f007590b790fd3a19f209b392a
Author: Aga Wronska <agawronska@chromium.org>
Date: Thu Jan 11 23:49:59 2018

Show system tray on views based shelf.

Add basic logic to show system tray from LoginScreenController. It
removes need for chrome control over this part of UI.

Do not show views based shelf in OOBE, because it still strongly relies
on web UI.

Bug:  792656 ,  798869 

Do not show views based shelf in OOBE.

Change-Id: Ia50695c44f9e78b7fc50c5e97dafd108ef1876a5
Reviewed-on: https://chromium-review.googlesource.com/848425
Commit-Queue: Aga Wronska <agawronska@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528818}
[modify] https://crrev.com/16abb43dd01897f007590b790fd3a19f209b392a/ash/login/login_screen_controller.cc
[modify] https://crrev.com/16abb43dd01897f007590b790fd3a19f209b392a/ash/login/login_screen_controller_unittest.cc
[modify] https://crrev.com/16abb43dd01897f007590b790fd3a19f209b392a/ash/shelf/login_shelf_view.cc
[modify] https://crrev.com/16abb43dd01897f007590b790fd3a19f209b392a/ash/shelf/shelf_widget.cc
[modify] https://crrev.com/16abb43dd01897f007590b790fd3a19f209b392a/ash/shelf/shelf_widget_unittest.cc
[modify] https://crrev.com/16abb43dd01897f007590b790fd3a19f209b392a/ash/system/status_area_widget.cc
[modify] https://crrev.com/16abb43dd01897f007590b790fd3a19f209b392a/ash/system/status_area_widget.h
[modify] https://crrev.com/16abb43dd01897f007590b790fd3a19f209b392a/ash/system/tray/system_tray_controller.cc
[modify] https://crrev.com/16abb43dd01897f007590b790fd3a19f209b392a/ui/login/display_manager.js

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cb8acabf1a5c456e34968981d46066b71240164b

commit cb8acabf1a5c456e34968981d46066b71240164b
Author: Quan Nguyen <qnnguyen@chromium.org>
Date: Wed Dec 05 20:39:08 2018

cros: Use the views-based shelf in OOBE.

As part of this CL, the following changes were made:
- The header-bar (md_header_bar.js) is always hidden
- The Gaia OOBE screen (screen_gaia_signin.js) manually controls the guest
  button visibility
- LoginScreenClient requests guest login directly instead of delegating
- Login shelf buttons change color to Google Grey 600 in OOBE (same as
  in webui shelf)
- Remove old redundant (and incorrect) showGuest condition in
  ExistingUserController
- Hard code mojom::OobeDialogState enum values. The ACCOUNT_PICKER state
  was present in display_manager.js but not mojom, and was causing
  dialog states after GAIA_SIGNIN from being reported incorrectly.
- Fix unit/browser tests to expect views login shelf.

Bug:  798869 
Change-Id: Ic032bae44c197a49fcf5ecfc59a04ef12b596629
Reviewed-on: https://chromium-review.googlesource.com/c/1352693
Commit-Queue: Quan Nguyen <qnnguyen@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614086}
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/login/login_screen_controller.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/login/login_screen_controller.h
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/login/login_screen_test_api.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/login/login_screen_test_api.h
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/login/ui/lock_screen.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/public/interfaces/login_screen.mojom
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/public/interfaces/login_screen_test_api.mojom
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/shelf/login_shelf_view.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/shelf/login_shelf_view.h
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/shelf/login_shelf_view_unittest.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/shelf/shelf_widget.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ash/shelf/shelf_widget_unittest.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/active_directory_login_browsertest.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/existing_user_controller.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/existing_user_controller_browsertest.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/lock/views_screen_locker.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/lock/views_screen_locker.h
[add] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/login_shelf_test_helper.cc
[add] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/login_shelf_test_helper.h
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/ui/login_display_host_mojo.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/ui/login_display_host_mojo.h
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/webview_login_browsertest.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/chromeos/login/wizard_controller_browsertest.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/resources/chromeos/login/screen_gaia_signin.js
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/ui/ash/login_screen_client.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/ui/ash/login_screen_client.h
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.h
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/chrome/test/BUILD.gn
[modify] https://crrev.com/cb8acabf1a5c456e34968981d46066b71240164b/ui/login/display_manager.js

Think this is basically fixed. Any bugs that pop up in the newer version should be new reports.