Detecting Browser Close or Tab Close without Impacting other functionality

I want to invalidate the session when the user close the tab or browser in my GWT Application. I saw lot of threads Confirm Browser Exit in GWT but didn't get the solution which i am looking for. This should not fire when user refresh the browser(it shouldn't invalidate the session) and even it should not fire when user navigate to other screen or download any file.Any Idea?

--
You received this message because you are subscribed to the Google Groups "GWT Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to google-web-toolkit+unsubscribe@googlegroups.com.
To post to this group, send email to google-web-toolkit@googlegroups.com.
Visit this group at https://groups.google.com/group/google-web-toolkit.
For more options, visit https://groups.google.com/d/optout.