Review-request for 8145547: JEP 283: [AWT/Swing] Conditional support for GTK 3 on Linux

[Semyon Sadetsky]

Hello,

Please review fix for JDK9:
bug: https://bugs.openjdk.java.net/browse/JDK-8145547
webrev: http://cr.openjdk.java.net/~ssadetsky/8145547/webrev.00/

The fix contains GTK3 based implementation for Swing GTK LnF, AWT 
FileChooser for Linux and AWT Robot for Linux.
Also the new system property is added to request specific GTK version 
swing.gtk.version.

--Semyon