Remove NOTIFICATION_SYSTEM_SETTING_CHANGED, switch CrosSettings to base::CallbackRegistry.

chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h

Index: chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
diff --git a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
index df9bf265bb8acc82eec8d01500475b77ef9e1e17..6f977d14fe9399c197eaac85d43754e03b3502d9 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
@@ -11,12 +11,14 @@
 #include "base/callback.h"
 #include "base/containers/hash_tables.h"
 #include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/chromeos/login/help_app_launcher.h"
 #include "chrome/browser/chromeos/login/login_display.h"
 #include "chrome/browser/chromeos/login/screens/error_screen_actor.h"
 #include "chrome/browser/chromeos/login/user_manager.h"
 #include "chrome/browser/chromeos/net/network_portal_detector.h"
+#include "chrome/browser/chromeos/settings/cros_settings.h"
 #include "chrome/browser/chromeos/system_key_event_listener.h"
 #include "chrome/browser/ui/webui/chromeos/login/base_screen_handler.h"
 #include "chrome/browser/ui/webui/chromeos/login/network_state_informer.h"
@@ -278,6 +280,7 @@ class SigninScreenHandler
 
   // Updates authentication extension. Called when device settings that affect
   // sign-in (allow BWSI and allow whitelist) are changed.
+  void UserSettingsChanged();
   void UpdateAuthExtension();
   void UpdateAddButtonStatus();
 
@@ -468,6 +471,9 @@ class SigninScreenHandler
   // NOTIFICATION_AUTH_CANCELLED.
   bool has_pending_auth_ui_;
 
+  scoped_ptr<CrosSettings::ObserverSubscription> allow_new_user_subscription_;
+  scoped_ptr<CrosSettings::ObserverSubscription> allow_guest_subscription_;
+
   DISALLOW_COPY_AND_ASSIGN(SigninScreenHandler);
 };