Move all typecasting code to individual screens.

chrome/browser/chromeos/login/screens/update_screen_browsertest.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 "base/command_line.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chromeos/login/screens/mock_error_screen.h"
 #include "chrome/browser/chromeos/login/screens/mock_screen_observer.h"
@@ skipping 62 matching lines @@
     mock_error_screen_.reset(
         new MockErrorScreen(mock_screen_observer_.get(),
                             mock_error_screen_actor_.get()));
     EXPECT_CALL(*mock_screen_observer_, ShowCurrentScreen())
         .Times(AnyNumber());
     EXPECT_CALL(*mock_screen_observer_, GetErrorScreen())
         .Times(AnyNumber())
         .WillRepeatedly(Return(mock_error_screen_.get()));
 
     ASSERT_TRUE(WizardController::default_controller() != NULL);
-    update_screen_ = WizardController::default_controller()->GetUpdateScreen();
+    update_screen_ = UpdateScreen::Get(WizardController::default_controller());
     ASSERT_TRUE(update_screen_ != NULL);
     ASSERT_EQ(WizardController::default_controller()->current_screen(),
               update_screen_);
     update_screen_->screen_observer_ = mock_screen_observer_.get();
   }
 
   virtual void TearDownOnMainThread() OVERRIDE {
     mock_error_screen_.reset();
     mock_error_screen_actor_.reset();
     WizardInProcessBrowserTest::TearDownOnMainThread();
@@ skipping 298 matching lines @@
       chromeos::UpdateEngineClient::UPDATE_RESULT_FAILED);
   EXPECT_CALL(*mock_screen_observer_,
               OnExit(ScreenObserver::UPDATE_ERROR_CHECKING_FOR_UPDATE))
       .Times(1);
 
   update_screen_->OnConnectToNetworkRequested();
   base::MessageLoop::current()->RunUntilIdle();
 }
 
 }  // namespace chromeos