Fix shelf visibility in kiosk splash screen

This cl hides shelf during splash screen, so users can't crash chrome
anymore :)

Bug: 1026638,1015383
Change-Id: I005006d470429176e4bb7830b80149a54e5ac691
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1926481Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Anatoliy Potapchuk <apotapchuk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#722424}

chrome/browser/chromeos/login/ui/login_display_host_mojo.cc

@@ -24,6 +24,7 @@
 #include "chrome/browser/chromeos/profiles/profile_helper.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/ash/login_screen_client.h"
+#include "chrome/browser/ui/ash/system_tray_client.h"
 #include "chrome/browser/ui/ash/wallpaper_controller_client.h"
 #include "chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.h"
 #include "chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h"
@@ -172,7 +173,7 @@ void LoginDisplayHostMojo::OnFinalize() {
 }
 
 void LoginDisplayHostMojo::SetStatusAreaVisible(bool visible) {
-  NOTIMPLEMENTED();
+  SystemTrayClient::Get()->SetPrimaryTrayVisible(visible);
 }
 
 void LoginDisplayHostMojo::StartWizard(OobeScreenId first_screen) {