<Swing Dev> [9] Review request for 8153351: GTK Menu's have no border

[Semyon Sadetsky]

Hello,

Please review fix for JDK9:
bug: https://bugs.openjdk.java.net/browse/JDK-8153351
webrev: http://cr.openjdk.java.net/~ssadetsky/8153351/webrev.00/

There are 2 issues here:
- so called "wide-separators" were not supported in GTK LnF. Metrics for 
those separators should be taken from another properties and they should 
be painted as boxes not lines. The fix adds supports for this GTK feature.
- The real insets of the popup menu should be taken into account when 
its background is painted, otherwise depending on the system theme there 
may be no space left for the popup menu border.
Since reproducible test scenario would require to setup the system theme 
the bug is labeled noreg-hard.

--Semyon