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..a15bce5273564f4da8eb1fee45e4b1e8856aa637 100644
--- a/chrome/browser/chromeos/login/screens/network_screen.cc
+++ b/chrome/browser/chromeos/login/screens/network_screen.cc
@@ -11,6 +11,7 @@
 #include "chrome/browser/chromeos/login/help_app_launcher.h"
 #include "chrome/browser/chromeos/login/helper.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/wizard_controller.h"
 #include "chrome/grit/chromium_strings.h"
@@ -31,6 +32,12 @@ 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),