[chromeos] Fix a use-after-free problem with LoginEventObserver

chrome/browser/automation/automation_event_observers_chromeos.cc

 // Copyright (c) 2012 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/automation/automation_event_observers.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chromeos/login/existing_user_controller.h"
 #include "content/public/browser/notification_service.h"
 
+using chromeos::ExistingUserController;
+
 LoginEventObserver::LoginEventObserver(
     AutomationEventQueue* event_queue,
-    chromeos::ExistingUserController* controller,
     AutomationProvider* automation)
     : AutomationEventObserver(event_queue, false),
-      controller_(controller),
       automation_(automation->AsWeakPtr()) {
-  controller_->set_login_status_consumer(this);
+  ExistingUserController* controller =
+      ExistingUserController::current_controller();
+  DCHECK(controller);
+  controller->set_login_status_consumer(this);
 }
 
 LoginEventObserver::~LoginEventObserver() {}
 
 void LoginEventObserver::OnLoginFailure(const chromeos::LoginFailure& error) {
   _NotifyLoginEvent(error.GetErrorString());
 }
 
 void LoginEventObserver::OnLoginSuccess(const std::string& username,
                                         const std::string& password,
@@ skipping 19 matching lines @@
     _NotifyLoginEvent(std::string());
   }
 }
 
 void LoginEventObserver::_NotifyLoginEvent(const std::string& error_string) {
   DictionaryValue* dict = new DictionaryValue;
   dict->SetString("type", "login_event");
   if (error_string.length())
     dict->SetString("error_string", error_string);
   NotifyEvent(dict);
-  controller_->set_login_status_consumer(NULL);
+  ExistingUserController* controller =
+      ExistingUserController::current_controller();
+  if (controller)
+    controller->set_login_status_consumer(NULL);
   RemoveIfDone();
 }