<Swing Dev> [9] Review request for 8160448: Make GTK3 menus appearence similar to native.

[Semyon Sadetsky]

Hello,

Please review fix for JDK9:

bug: https://bugs.openjdk.java.net/browse/JDK-8160448

webrev: http://cr.openjdk.java.net/~ssadetsky/8160448/webrev.00/

GTK3 lib uses has several specific features in the menu painting that 
differs from GTK2 approach. The solution implements those features to 
follow the native menu appearance.

Test would require native code, so noreg-hard label is used.

--Semyon