Add gtk_native_dialog_destroy()

Its very easy to get extra references to the NativeDialog so that
when you release your last reference any visible dialog is not
hidden. We handle this by adding a destroy method similar to how
you destroy regular toplevels.

demos/gtk-demo/application.c

@@ -113,6 +113,7 @@ open_response_cb (GtkNativeDialog *dialog,
         }
     }
 
+  gtk_native_dialog_destroy (GTK_NATIVE_DIALOG (native));
   g_object_unref (native);
 }
 

docs/reference/gtk/gtk3-sections.txt

@@ -2520,6 +2520,7 @@ GTK_TYPE_NATIVE_DIALOG
 GtkNativeDialogClass
 gtk_native_dialog_show
 gtk_native_dialog_hide
+gtk_native_dialog_destroy
 gtk_native_dialog_get_visible
 gtk_native_dialog_set_modal
 gtk_native_dialog_get_modal

gtk/gtkfilechooserbutton.c

@@ -1008,7 +1008,11 @@ gtk_file_chooser_button_destroy (GtkWidget *widget)
       priv->dialog = NULL;
     }
 
+  if (priv->native)
+    {
+      gtk_native_dialog_destroy (GTK_NATIVE_DIALOG (priv->native));
       g_clear_object (&priv->native);
+    }
 
   priv->chooser = NULL;
 

gtk/gtknativedialog.c

@@ -361,6 +361,30 @@ gtk_native_dialog_hide (GtkNativeDialog *self)
   g_object_notify_by_pspec (G_OBJECT (self), native_props[PROP_VISIBLE]);
 }
 
+/**
+ * gtk_native_dialog_destroy:
+ * @self: a #GtkNativeDialog
+ *
+ * Destroys a dialog.
+ *
+ * When a dialog is destroyed, it will break any references it holds
+ * to other objects. If it is visible it will be hidden and any underlying
+ * window system resources will be destroyed.
+ *
+ * Note that this does not release any reference to the object (as opposed to
+ * destroying a GtkWindow) because there is no reference from the windowing
+ * system to the #GtkNativeDialog.
+ *
+ * Since: 3.20
+ **/
+void
+gtk_native_dialog_destroy (GtkNativeDialog *self)
+{
+  g_return_if_fail (GTK_IS_NATIVE_DIALOG (self));
+
+  g_object_run_dispose (G_OBJECT (self));
+}
+
 void
 _gtk_native_dialog_emit_response (GtkNativeDialog *self,
                                   int response_id)

gtk/gtknativedialog.h

@@ -54,6 +54,8 @@ void                  gtk_native_dialog_show (GtkNativeDialog *self);
 GDK_AVAILABLE_IN_3_20
 void                  gtk_native_dialog_hide (GtkNativeDialog *self);
 GDK_AVAILABLE_IN_3_20
+void                  gtk_native_dialog_destroy (GtkNativeDialog *self);
+GDK_AVAILABLE_IN_3_20
 gboolean              gtk_native_dialog_get_visible (GtkNativeDialog *self);
 GDK_AVAILABLE_IN_3_20
 void                  gtk_native_dialog_set_modal (GtkNativeDialog *self,

tests/testgtk.c

@@ -9660,6 +9660,13 @@ native_filter_changed (GtkWidget *combo,
     }
 }
 
+static void
+destroy_native (GtkFileChooserNative *native)
+{
+  gtk_native_dialog_destroy (GTK_NATIVE_DIALOG (native));
+  g_object_unref (native);
+}
+
 void
 create_native_dialogs (GtkWidget *widget)
 {
@@ -9681,7 +9688,7 @@ create_native_dialogs (GtkWidget *widget)
                                             "_accept&native",
                                             "_cancel__native");
 
-      g_signal_connect_swapped (G_OBJECT (window), "destroy", G_CALLBACK (g_object_unref), native);
+      g_signal_connect_swapped (G_OBJECT (window), "destroy", G_CALLBACK (destroy_native), native);
 
       gtk_file_chooser_add_shortcut_folder (GTK_FILE_CHOOSER (native),
                                             g_get_current_dir (),