Prevents session_length_timeout reappearing when it's already dismissed.

ash/system/session_length_limit/tray_session_length_limit.cc

Index: ash/system/session_length_limit/tray_session_length_limit.cc
diff --git a/ash/system/session_length_limit/tray_session_length_limit.cc b/ash/system/session_length_limit/tray_session_length_limit.cc
index af32635bb9b5f1a1036309c53e79d66030b81ad6..90b088d1602e9a9338c27807267aee86f40e403d 100644
--- a/ash/system/session_length_limit/tray_session_length_limit.cc
+++ b/ash/system/session_length_limit/tray_session_length_limit.cc
@@ -78,6 +78,15 @@ base::string16 FormatRemainingSessionTimeNotification(
 
 void CreateOrUpdateNotification(const base::TimeDelta& remaining_time,
                                 bool enable_spoken_feedback) {
+  message_center::MessageCenter* message_center =
+      message_center::MessageCenter::Get();
+  // If |enable_spoken_feedback| is false, it's just an update of the content,
+  // which should not create a new one if it's already closed.

[stevenjb, 2013/09/09 17:58:03]

nit: s/one/notification

[Jun Mukai, 2013/09/09 19:37:25]

Done.

+  if (!enable_spoken_feedback &&
+      !message_center->HasNotification(kSessionLengthTimeoutNotificationId)) {

[stevenjb, 2013/09/09 17:58:03]

This seems awkward; we're effectively using 'enable_spoken_feedback' as
'create'. I think it would be more clear if this logic were moved to Update().

[Jun Mukai, 2013/09/09 19:37:25]

I don't think I need to separate the function / logic here, instead rename the
|enable_spoken_feedback| flag to another name, |state_changed|.

[stevenjb, 2013/09/09 19:43:07]

OK, that's more clear now.

+    return;
+  }
+
   ui::ResourceBundle& bundle = ui::ResourceBundle::GetSharedInstance();
   message_center::RichNotificationData data;
   data.should_make_spoken_feedback_for_popup_updates = enable_spoken_feedback;