Move all typecasting code to individual screens.

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

Index: chrome/browser/chromeos/login/screens/user_image_screen.cc
diff --git a/chrome/browser/chromeos/login/screens/user_image_screen.cc b/chrome/browser/chromeos/login/screens/user_image_screen.cc
index bd709db795b5b4a1080aba28b7ecd35f8ede4ff3..3ae23f99a25d91a16183f34019e0c4ddea265c4d 100644
--- a/chrome/browser/chromeos/login/screens/user_image_screen.cc
+++ b/chrome/browser/chromeos/login/screens/user_image_screen.cc
@@ -19,6 +19,7 @@
 #include "chrome/browser/chromeos/accessibility/accessibility_manager.h"
 #include "chrome/browser/chromeos/camera_presence_notifier.h"
 #include "chrome/browser/chromeos/login/login_utils.h"
+#include "chrome/browser/chromeos/login/screen_manager.h"
 #include "chrome/browser/chromeos/login/screens/screen_observer.h"
 #include "chrome/browser/chromeos/login/users/avatar/user_image_manager.h"
 #include "chrome/browser/chromeos/login/users/chrome_user_manager.h"
@@ -57,6 +58,12 @@ const int kSyncTimeoutSeconds = 10;
 
 }  // namespace
 
+// static
+UserImageScreen* UserImageScreen::Get(ScreenManager* manager) {
+  return static_cast<UserImageScreen*>(
+      manager->GetScreen(WizardController::kUserImageScreenName));
+}
+
 UserImageScreen::UserImageScreen(ScreenObserver* screen_observer,
                                  UserImageScreenActor* actor)
     : WizardScreen(screen_observer),