JFileChooser combobox doesn't have focus border unlike native mercury.

Steps to Reproduce:
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1) Run SwingSet2 on Mercury with -Dswing.gtkthemefile=<Your .gtkrc File>. Change the Look And Feel to GTK.
2) Go to FileChooser Demo.
3) Click on button 'Show Plain JFileChooser' and now tab to combo box so that it have focus, But it still don't show focus border.
4) Now open Gedit.
5) Click Open and now tab to combo box so that it have focus, It shows focus border. It is different than java implementation of the same.