button: Add private api to get the gesture

This may be used by subclasses who need to group
their gestures with the button gesture.

gtk/gtkbutton.c

@@ -435,7 +435,6 @@ gtk_button_init (GtkButton *button)
   g_signal_connect (priv->gesture, "update", G_CALLBACK (multipress_gesture_update_cb), button);
   g_signal_connect (priv->gesture, "cancel", G_CALLBACK (multipress_gesture_cancel_cb), button);
   gtk_event_controller_set_propagation_phase (GTK_EVENT_CONTROLLER (priv->gesture), GTK_PHASE_CAPTURE);
-
 }
 
 static void
@@ -1146,3 +1145,11 @@ gtk_button_get_icon_name (GtkButton *button)
 
   return NULL;
 }
+
+GtkGesture *
+gtk_button_get_gesture (GtkButton *button)
+{
+  GtkButtonPrivate *priv = gtk_button_get_instance_private (button);
+
+  return priv->gesture;
+}

gtk/gtkbuttonprivate.h

@@ -41,6 +41,7 @@ struct _GtkButtonPrivate
   guint          child_type            : 2;
 };
 
+GtkGesture *gtk_button_get_gesture (GtkButton *button);
 
 G_END_DECLS