[gspell] Make GspellCheckerDialog derivable

[Sébastien Wilmet <swilmet src gnome org>]

commit 4f7fb96c7055ba4a4371b00d8b45e4048187a4d5
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Thu Nov 19 15:09:00 2015 +0100

    Make GspellCheckerDialog derivable
    
    I don't think it'll be really useful, but a GtkDialog is usually
    derivable.

 gspell/gspell-checker-dialog.c |    5 -----
 gspell/gspell-checker-dialog.h |   14 +++++++++++---
 2 files changed, 11 insertions(+), 8 deletions(-)
---
diff --git a/gspell/gspell-checker-dialog.c b/gspell/gspell-checker-dialog.c
index 0ea8e3f..720e6b1 100644
--- a/gspell/gspell-checker-dialog.c
+++ b/gspell/gspell-checker-dialog.c
@@ -35,11 +35,6 @@
 
 typedef struct _GspellCheckerDialogPrivate GspellCheckerDialogPrivate;
 
-struct _GspellCheckerDialog
-{
-       GtkDialog parent_instance;
-};
-
 struct _GspellCheckerDialogPrivate
 {
        GspellNavigator *navigator;
diff --git a/gspell/gspell-checker-dialog.h b/gspell/gspell-checker-dialog.h
index f131b07..e40cfd8 100644
--- a/gspell/gspell-checker-dialog.h
+++ b/gspell/gspell-checker-dialog.h
@@ -27,9 +27,17 @@
 G_BEGIN_DECLS
 
 #define GSPELL_TYPE_CHECKER_DIALOG (gspell_checker_dialog_get_type ())
-G_DECLARE_FINAL_TYPE (GspellCheckerDialog, gspell_checker_dialog,
-                     GSPELL, CHECKER_DIALOG,
-                     GtkDialog)
+G_DECLARE_DERIVABLE_TYPE (GspellCheckerDialog, gspell_checker_dialog,
+                         GSPELL, CHECKER_DIALOG,
+                         GtkDialog)
+
+struct _GspellCheckerDialogClass
+{
+       GtkDialogClass parent_class;
+
+       /* Padding for future expansion */
+       gpointer padding[8];
+};
 
 GtkWidget *    gspell_checker_dialog_new               (GtkWindow       *parent,
                                                         GspellNavigator *navigator);