[8u40] post-commit review: RT-38457: Creating a ContextMenu on the JavaFX-Launcher thread causes an IllegalStateException

[Kevin Rushforth]

Post-commit review for:

JIRA:  https://javafx-jira.kenai.com/browse/RT-38457
Changeset:  http://hg.openjdk.java.net/openjfx/8u-dev/rt/rev/5e65b34a175b

This fixes a problem that was exposed by the fix for 
https://javafx-jira.kenai.com/browse/RT-17716 and is needed to allow 
creation of ContextMenu and Toolip prior to the start method from being 
called (prior to the creation of the first Stage).

-- Kevin