[gnome-shell] extensionPrefs: Fix pref button appearance

[Florian Müllner <fmuellner src gnome org>]

commit 5d9f80bc735921089d2a5c03d84264d5df883c57
Author: Florian Müllner <fmuellner gnome org>
Date:   Fri Apr 5 18:24:09 2019 +0200

    extensionPrefs: Fix pref button appearance
    
    After the Adwaita refresh, the button shows up oval rather than
    circular. To address this, make sure that the "image-button" class
    is applied as well by using the dedicated setter function.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/482

 js/extensionPrefs/main.js | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/js/extensionPrefs/main.js b/js/extensionPrefs/main.js
index 438788f1d..43efa95e9 100644
--- a/js/extensionPrefs/main.js
+++ b/js/extensionPrefs/main.js
@@ -551,9 +551,9 @@ class ExtensionRow extends Gtk.ListBoxRow {
 
         let button = new Gtk.Button({ valign: Gtk.Align.CENTER,
                                       no_show_all: true });
-        button.add(new Gtk.Image({ icon_name: 'emblem-system-symbolic',
-                                   icon_size: Gtk.IconSize.BUTTON,
-                                   visible: true }));
+        button.set_image(new Gtk.Image({ icon_name: 'emblem-system-symbolic',
+                                         icon_size: Gtk.IconSize.BUTTON,
+                                         visible: true }));
         button.get_style_context().add_class('circular');
         hbox.add(button);