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

ash/system/tray/system_tray.cc

Index: ash/system/tray/system_tray.cc
diff --git a/ash/system/tray/system_tray.cc b/ash/system/tray/system_tray.cc
index 5870e5500c0d8610897fd92661fbd4bd1c3d3ad5..1a98a7c239b6bde1d11a0819db472eadd39c242a 100644
--- a/ash/system/tray/system_tray.cc
+++ b/ash/system/tray/system_tray.cc
@@ -498,17 +498,9 @@ void SystemTray::UpdateAfterLoginStatusChange(user::LoginStatus login_status) {
   for (std::vector<SystemTrayItem*>::iterator it = items_.begin();
       it != items_.end();
       ++it) {
-    (*it)->DestroyTrayView();
+    (*it)->UpdateAfterLoginStatusChange(login_status);
   }
-  container_->RemoveAllChildViews(true);
 
-  for (std::vector<SystemTrayItem*>::iterator it = items_.begin();
-      it != items_.end();
-      ++it) {
-    views::View* view = (*it)->CreateTrayView(login_status);
-    if (view)
-      container_->AddChildViewAt(view, 0);
-  }
   SetVisible(true);
   PreferredSizeChanged();
 }