Move all typecasting code to individual screens.

chrome/browser/chromeos/login/enrollment/enrollment_screen.h

Index: chrome/browser/chromeos/login/enrollment/enrollment_screen.h
diff --git a/chrome/browser/chromeos/login/enrollment/enrollment_screen.h b/chrome/browser/chromeos/login/enrollment/enrollment_screen.h
index 48a7b8d5b3232f34af11f6d46594e8165ce64bb3..d2d8516be2a67c1285d83882fda8f23f90ab38d8 100644
--- a/chrome/browser/chromeos/login/enrollment/enrollment_screen.h
+++ b/chrome/browser/chromeos/login/enrollment/enrollment_screen.h
@@ -18,6 +18,7 @@
 
 namespace chromeos {
 
+class ScreenManager;
 class ScreenObserver;
 
 // The screen implementation that links the enterprise enrollment UI into the
@@ -30,6 +31,8 @@ class EnrollmentScreen
                    EnrollmentScreenActor* actor);
   virtual ~EnrollmentScreen();
 
+  static EnrollmentScreen* Get(ScreenManager* manager);
+
   void SetParameters(EnrollmentScreenActor::EnrollmentMode enrollment_mode,
                      const std::string& management_domain,
                      const std::string& enrollment_user,