Move all typecasting code to individual screens.

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

Index: chrome/browser/chromeos/login/screens/network_screen.cc
diff --git a/chrome/browser/chromeos/login/screens/network_screen.cc b/chrome/browser/chromeos/login/screens/network_screen.cc
index 193aa675dc80db870eecf7bf46f30c8280168255..2b3735e757080ee2bbb22f008a395c9a1c9f4235 100644
--- a/chrome/browser/chromeos/login/screens/network_screen.cc
+++ b/chrome/browser/chromeos/login/screens/network_screen.cc
@@ -31,6 +31,12 @@ namespace chromeos {
 ///////////////////////////////////////////////////////////////////////////////
 // NetworkScreen, public:
 
+// static
+NetworkScreen* NetworkScreen::Get(ScreenManager* manager) {
+  return static_cast<NetworkScreen*>(
+      manager->GetScreen(WizardController::kNetworkScreenName));
+}
+
 NetworkScreen::NetworkScreen(ScreenObserver* screen_observer,
                              NetworkScreenActor* actor)
     : WizardScreen(screen_observer),