[9, 8] Review request for 8081485: EDT auto shutdown is broken in case of new event queue usage

[Anton Nashatyrev]

Hello Artem, Sergey

    thanks for your help with the issue investigation!
    could you please review the following fix:

fix: http://cr.openjdk.java.net/~anashaty/8081485/webrev.00/ 
<http://cr.openjdk.java.net/%7Eanashaty/8081485/webrev.00/>
bug: 
https://bugs.openjdk.java.net/browse/JDK-8081485<https://bugs.openjdk.java.net/browse/JDK-8025145>

    Problem: EventQueue.push() at the very beginning prevents the app 
from shutting down automatically

    Reason: the EventQueue.push() first checks if the EDT for the top 
EventQeue exists (to transfer it to the new EventQueue) and then 
implicitly starts it.

    Fix: do posting of dummy event only in case if the EventQueue had 
the EDT

Thanks!
Anton.