[8u60] Request for review: RT-40385: [Mac] NPE in window close unit tests

[Kevin Rushforth]

As a reminder, bug fixes should go into 9-dev before (or at the same 
time) as into 8u-dev.

-- Kevin


Morris Meyer wrote:
> David and Kevin,
>
> Please review my fix for the recent regression caused by my fix for 
> RT-39813.  Both changes crop up in the systemTests and are necessary 
> to adjust for the close sequence timing change introduced in RT-39813.
>
> Tested using:
>
> gradle -PFULL_TEST=true :systemTests:test
>
> Thanks much.
>
>         --morris
>
> WEBREV - http://cr.openjdk.java.net/~morris/RT-40385.01/
> JIRA - https://javafx-jira.kenai.com/browse/RT-40385