Fix chromium crash after setting up policy for device disable

In the condition when the device is disabled by policy it was referencing a yet
uninitialized LoginScreenClient leading to SYSSEGV and boot/login loop in
Chromebooks.

Bug: 884127
Change-Id: If99d945777e56cbc1299f5094afd32cee1872f3a
Reviewed-on: https://chromium-review.googlesource.com/c/1435436
Commit-Queue: Anatoliy Potapchuk <apotapchuk@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626120}

chrome/browser/chromeos/chrome_browser_main_chromeos.cc

@@ -930,7 +930,6 @@ void ChromeBrowserMainPartsChromeos::PostProfileInit() {
       g_browser_process->local_state());
 
   g_browser_process->platform_part()->InitializeAutomaticRebootManager();
-  g_browser_process->platform_part()->InitializeDeviceDisablingManager();
   user_removal_manager::RemoveUsersIfNeeded();
 
   // This observer cannot be created earlier because it requires the shell to be

chrome/browser/chromeos/login/lock/screen_locker.cc

@@ -214,6 +214,7 @@ void ScreenLocker::Init() {
     delegate_ = views_screen_locker_.get();
 
     // Create and display lock screen.
+    CHECK(LoginScreenClient::HasInstance());
     LoginScreenClient::Get()->login_screen()->ShowLockScreen(base::BindOnce(
         [](ViewsScreenLocker* screen_locker, bool did_show) {
           CHECK(did_show);

chrome/browser/ui/ash/chrome_browser_main_extra_parts_ash.cc

@@ -271,6 +271,9 @@ void ChromeBrowserMainExtraPartsAsh::PostProfileInit() {
   cast_config_client_media_router_ =
       std::make_unique<CastConfigClientMediaRouter>();
   login_screen_client_ = std::make_unique<LoginScreenClient>();
+  // https://crbug.com/884127 ensuring that LoginScreenClient is initialized before using it InitializeDeviceDisablingManager.
+  g_browser_process->platform_part()->InitializeDeviceDisablingManager();
+
   media_client_ = std::make_unique<MediaClient>();
 
   // Instantiate DisplaySettingsHandler after CrosSettings has been