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

ash/system/network/tray_network.cc

Index: ash/system/network/tray_network.cc
diff --git a/ash/system/network/tray_network.cc b/ash/system/network/tray_network.cc
index f3aedef6538addd8e2e24f79570ab035e8da22ea..55847d1a63bacabb15bb0c2d8b981759be0fb85a 100644
--- a/ash/system/network/tray_network.cc
+++ b/ash/system/network/tray_network.cc
@@ -517,6 +517,9 @@ void TrayNetwork::DestroyDetailedView() {
   detailed_.reset();
 }
 
+void TrayNetwork::UpdateAfterLoginStatusChange(user::LoginStatus status) {
+}
+
 void TrayNetwork::OnNetworkRefresh(const NetworkIconInfo& info) {
   if (tray_.get())
     tray_->Update(info);