Implements the dialog view for logout button tray in public sessions.

ash/system/tray/system_tray_notifier.cc

Index: ash/system/tray/system_tray_notifier.cc
diff --git a/ash/system/tray/system_tray_notifier.cc b/ash/system/tray/system_tray_notifier.cc
index e2035ad357feac1cf666d476d936a5477be47190..95b6789e87d75d0fe91ee6cddbf5e2ec33123a18 100644
--- a/ash/system/tray/system_tray_notifier.cc
+++ b/ash/system/tray/system_tray_notifier.cc
@@ -232,6 +232,13 @@ void SystemTrayNotifier::NotifyShowLoginButtonChanged(bool show_login_button) {
                     OnShowLogoutButtonInTrayChanged(show_login_button));
 }
 
+void SystemTrayNotifier::NotifyLogoutDialogDurationChanged(
+    base::TimeDelta duration) {
+  FOR_EACH_OBSERVER(LogoutButtonObserver,
+                    logout_button_observers_,
+                    OnLogoutDialogDurationChanged(duration));
+}
+
 void SystemTrayNotifier::NotifyLocaleChanged(
     LocaleObserver::Delegate* delegate,
     const std::string& cur_locale,