Move all typecasting code to individual screens.

chrome/browser/chromeos/login/supervised/supervised_user_creation_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/supervised/supervised_user_creation_screen.h"
 
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "ash/shell.h"
 #include "base/rand_util.h"
 #include "base/values.h"
@@ skipping 67 matching lines @@
                             std::string());
       break;
     default:
       NOTREACHED();
       break;
   }
 }
 
 } // namespace
 
+// static
+SupervisedUserCreationScreen* SupervisedUserCreationScreen::Get(
+    ScreenManager* manager) {
+  return static_cast<SupervisedUserCreationScreen*>(
+      manager->GetScreen(WizardController::kSupervisedUserCreationScreenName));
+}
+
 SupervisedUserCreationScreen::SupervisedUserCreationScreen(
     ScreenObserver* observer,
     SupervisedUserCreationScreenHandler* actor)
     : WizardScreen(observer),
       weak_factory_(this),
       actor_(actor),
       on_error_screen_(false),
       last_page_(kNameOfIntroScreen),
       sync_service_(NULL),
       image_decoder_(NULL),
@@ skipping 496 matching lines @@
     selected_image_ = user_manager::User::USER_IMAGE_EXTERNAL;
   } else {
     NOTREACHED() << "Unexpected image type: " << image_type;
   }
 }
 
 void SupervisedUserCreationScreen::OnImageAccepted() {
 }
 
 }  // namespace chromeos