ash: Refresh the tray items, instead of recreating them, when login status changes.

ash/system/date/tray_date.cc

Index: ash/system/date/tray_date.cc
diff --git a/ash/system/date/tray_date.cc b/ash/system/date/tray_date.cc
index bead9706504f992cb4c546cb40b79b85e00d4955..fb8d82954cf26eb239c0ef60f0fec25f251a0ebe 100644
--- a/ash/system/date/tray_date.cc
+++ b/ash/system/date/tray_date.cc
@@ -73,6 +73,9 @@ void TrayDate::DestroyDefaultView() {
 void TrayDate::DestroyDetailedView() {
 }
 
+void TrayDate::UpdateAfterLoginStatusChange(user::LoginStatus status) {
+}
+
 void TrayDate::OnDateFormatChanged() {
   date_tray_->UpdateTimeFormat();
 }