Code Review Request For RT-38808:[JFXPanel, Mac] Popups causes JRE crash

[Chien Yang]

Hi Kevin and Steve,

Please review the revised fix. Stress test programs and more information 
are in the JIRA:

https://javafx-jira.kenai.com/browse/RT-38808

Hi Anton and Morris,

We need to test this fix on more Mac machines. Can you kindly run the 
stress test programs on your Mac with and without the proposed fix, and 
report your finding in the JIRA?

Thanks,
- Chien