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

ash/system/tray/tray_image_item.cc

Index: ash/system/tray/tray_image_item.cc
diff --git a/ash/system/tray/tray_image_item.cc b/ash/system/tray/tray_image_item.cc
index 9e92e0c8a6cb97db5b8cb21b3d428cd979084e1b..238cb0cd177243b5a7856ed34bcb63889ccc9290 100644
--- a/ash/system/tray/tray_image_item.cc
+++ b/ash/system/tray/tray_image_item.cc
@@ -40,6 +40,9 @@ views::View* TrayImageItem::CreateDetailedView(user::LoginStatus status) {
   return NULL;
 }
 
+void TrayImageItem::UpdateAfterLoginStatusChange(user::LoginStatus status) {
+}
+
 void TrayImageItem::DestroyTrayView() {
   tray_view_.reset();
 }