hg: jdk/jdk13: 8226783: GTK is not being returned as the System L&F on Gnome

[philip.race at oracle.com]

Changeset: f6d6fd388315
Author:    prr
Date:      2019-06-27 12:55 -0700
URL:       http://hg.openjdk.java.net/jdk/jdk13/rev/f6d6fd388315

8226783: GTK is not being returned as the System L&F on Gnome
Reviewed-by: serb, psadhukhan

! src/java.desktop/unix/classes/sun/awt/UNIXToolkit.java
+ test/jdk/javax/swing/LookAndFeel/SystemLookAndFeel/SystemLookAndFeelTest.java