Add a missing call to NULL-ify the delegate of the AutoEnrollmentScreen.

chrome/browser/chromeos/login/enrollment/auto_enrollment_check_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/enrollment/auto_enrollment_check_screen.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 12 matching lines @@
       actor_(actor),
       captive_portal_status_(
           NetworkPortalDetector::CAPTIVE_PORTAL_STATUS_UNKNOWN),
       auto_enrollment_state_(policy::AUTO_ENROLLMENT_STATE_IDLE) {
   if (actor_)
     actor_->SetDelegate(this);
 }
 
 AutoEnrollmentCheckScreen::~AutoEnrollmentCheckScreen() {
   NetworkPortalDetector::Get()->RemoveObserver(this);
+  if (actor_)
+    actor_->SetDelegate(NULL);
 }
 
 void AutoEnrollmentCheckScreen::Start() {
   if (!IsStartNeeded())
     return;
 
   // Make sure the auto-enrollment client is running.
   auto_enrollment_controller_->Start();
 
   auto_enrollment_progress_subscription_ =
@@ skipping 169 matching lines @@
 }
 
 void AutoEnrollmentCheckScreen::SignalCompletion() {
   NetworkPortalDetector::Get()->RemoveObserver(this);
   auto_enrollment_progress_subscription_.reset();
   get_screen_observer()->OnExit(
       ScreenObserver::ENTERPRISE_AUTO_ENROLLMENT_CHECK_COMPLETED);
 }
 
 }  // namespace chromeos