range: Add private api to get the trough node

This will be needed in range subclasses to position their
own subnodes.

gtk/gtkrange.c

@@ -4317,3 +4317,9 @@ _gtk_range_set_steppers (GtkRange *range,
 
   gtk_widget_queue_resize (GTK_WIDGET (range));
 }
+
+GtkCssNode *
+gtk_range_get_trough_node (GtkRange *range)
+{
+  return range->priv->trough_node;
+}

gtk/gtkrangeprivate.h

@@ -27,6 +27,7 @@
 
 
 #include <gtk/gtkrange.h>
+#include <gtk/gtkcssnodeprivate.h>
 
 
 G_BEGIN_DECLS
@@ -47,6 +48,8 @@ void               _gtk_range_set_steppers                 (GtkRange      *range
                                                             gboolean       has_c,
                                                             gboolean       has_d);
 
+GtkCssNode        *gtk_range_get_trough_node (GtkRange *range);
+
 G_END_DECLS