Move all typecasting code to individual screens.

chrome/browser/chromeos/login/screens/user_image_screen.h

Index: chrome/browser/chromeos/login/screens/user_image_screen.h
diff --git a/chrome/browser/chromeos/login/screens/user_image_screen.h b/chrome/browser/chromeos/login/screens/user_image_screen.h
index 5783e29c89ba906f25c61a1aaa3d94bfdc135bff..47e4add9c71a4eb3abf40d024b20f27e4d8206d7 100644
--- a/chrome/browser/chromeos/login/screens/user_image_screen.h
+++ b/chrome/browser/chromeos/login/screens/user_image_screen.h
@@ -28,6 +28,7 @@ class PolicyChangeRegistrar;
 namespace chromeos {
 
 class UserImageManager;
+class ScreenManager;
 
 class UserImageScreen: public WizardScreen,
                        public UserImageScreenActor::Delegate,
@@ -40,6 +41,8 @@ class UserImageScreen: public WizardScreen,
                   UserImageScreenActor* actor);
   virtual ~UserImageScreen();
 
+  static UserImageScreen* Get(ScreenManager* manager);
+
   // WizardScreen implementation:
   virtual void PrepareToShow() OVERRIDE;
   virtual void Show() OVERRIDE;