Remove NOTIFICATION_SYSTEM_SETTING_CHANGED, switch CrosSettings to base::CallbackRegistry.

chrome/browser/chromeos/login/user_manager_impl.h

Index: chrome/browser/chromeos/login/user_manager_impl.h
diff --git a/chrome/browser/chromeos/login/user_manager_impl.h b/chrome/browser/chromeos/login/user_manager_impl.h
index 09a6361b0a09b903b88bfdc4a5d884637b5bf5d3..0ba939c022681bb3be2ae1b05a72c68a1e862da9 100644
--- a/chrome/browser/chromeos/login/user_manager_impl.h
+++ b/chrome/browser/chromeos/login/user_manager_impl.h
@@ -398,6 +398,11 @@ class UserManagerImpl
   // Time at which this object was created.
   base::TimeTicks manager_creation_time_;
 
+  scoped_ptr<CrosSettings::ObserverSubscription>
+      local_accounts_subscription_;
+  scoped_ptr<CrosSettings::ObserverSubscription>
+      supervised_users_subscription_;
+
   DISALLOW_COPY_AND_ASSIGN(UserManagerImpl);
 };