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

ash/system/power/tray_power.cc

Index: ash/system/power/tray_power.cc
diff --git a/ash/system/power/tray_power.cc b/ash/system/power/tray_power.cc
index ee0229f7402a7b736386f5b8201d74d52729834a..6c969d114cb83b3dd2c675e66f0654a2b89a3a8c 100644
--- a/ash/system/power/tray_power.cc
+++ b/ash/system/power/tray_power.cc
@@ -243,6 +243,9 @@ void TrayPower::DestroyDefaultView() {
 void TrayPower::DestroyDetailedView() {
 }
 
+void TrayPower::UpdateAfterLoginStatusChange(user::LoginStatus status) {
+}
+
 void TrayPower::OnPowerStatusChanged(const PowerSupplyStatus& status) {
   if (power_tray_.get())
     power_tray_->UpdatePowerStatus(status);