widget: Add _gtk_widget_peek_accessible()

This function returns the accessible if it already exists. This way we
can call functions on the accessible from the widget itself instead of
having to rely on signals.

gtk/gtkwidget.c

@@ -11289,6 +11289,25 @@ gtk_widget_class_set_accessible_role (GtkWidgetClass *widget_class,
   priv->accessible_role = role;
 }
 
+/**
+ * _gtk_widget_peek_accessible:
+ * @widget: a #GtkWidget
+ *
+ * Gets the accessible for @widget, if it has been created yet.
+ * Otherwise, this function returns %NULL. If the @widget's implementation
+ * does not use the default way to create accessibles, %NULL will always be
+ * returned.
+ *
+ * Returns: the accessible for @widget or %NULL if none has been
+ *     created yet.
+ **/
+AtkObject *
+_gtk_widget_peek_accessible (GtkWidget *widget)
+{
+  return g_object_get_qdata (G_OBJECT (widget),
+                             quark_accessible_object);
+}
+
 /**
  * gtk_widget_get_accessible:
  * @widget: a #GtkWidget

gtk/gtkwidgetprivate.h

@@ -118,6 +118,8 @@ void     _gtk_widget_free_cached_sizes (GtkWidget *widget);
 const gchar*      _gtk_widget_get_accel_path               (GtkWidget *widget,
                                                             gboolean  *locked);
 
+AtkObject *       _gtk_widget_peek_accessible              (GtkWidget *widget);
+
 GdkEventExpose *  _gtk_cairo_get_event                     (cairo_t *cr);
 
 void              _gtk_widget_draw_internal                (GtkWidget *widget,