Add DeviceADPolicyManager to provide AD policy.

chrome/browser/chromeos/login/screens/chrome_user_selection_screen.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/login/screens/chrome_user_selection_screen.h"
 
 #include <memory>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 22 matching lines @@
 
 namespace chromeos {
 
 ChromeUserSelectionScreen::ChromeUserSelectionScreen(
     const std::string& display_type)
     : UserSelectionScreen(display_type),
       handler_initialized_(false),
       weak_factory_(this) {
   device_local_account_policy_service_ = g_browser_process->platform_part()->
       browser_policy_connector_chromeos()->GetDeviceLocalAccountPolicyService();
-  device_local_account_policy_service_->AddObserver(this);
+  if (device_local_account_policy_service_) {
+    device_local_account_policy_service_->AddObserver(this);
+  }
 }
 
 ChromeUserSelectionScreen::~ChromeUserSelectionScreen() {
-  device_local_account_policy_service_->RemoveObserver(this);
+  if (device_local_account_policy_service_) {
+    device_local_account_policy_service_->RemoveObserver(this);
+  }
 }
 
 void ChromeUserSelectionScreen::Init(const user_manager::UserList& users,
                                      bool show_guest) {
   UserSelectionScreen::Init(users, show_guest);
 
   // Retrieve the current policy for all users.
   for (user_manager::UserList::const_iterator it = users.begin();
        it != users.end(); ++it) {
     if ((*it)->GetType() == user_manager::USER_TYPE_PUBLIC_ACCOUNT)
@@ skipping 126 matching lines @@
   // advanced form (two or more recommended locales).
   const bool two_or_more_recommended_locales = recommended_locales.size() >= 2;
 
   // Notify the UI.
   view_->SetPublicSessionLocales(account_id, std::move(available_locales),
                                  default_locale,
                                  two_or_more_recommended_locales);
 }
 
 }  // namespace chromeos