[9] Review Request:: 8029536 JFileChooser filter uses .toString() instead of getDescription() for filter text on GTK laf

[Sergey Bylokhov]

Hello.
Please review the fix for jdk 9.
The fix is very simple: the GTKFileChooserUI.FilterComboBoxRenderer 
class must not implement UIResource (see similar classes in other L&Fs).

Bug: https://bugs.openjdk.java.net/browse/JDK-8029536
Webrev can be found at: http://cr.openjdk.java.net/~serb/8029536/webrev.00

--
Best regards, Sergey.