Organize Iris support files

src/rsc/sense_tests.rs

@@ -101,7 +101,7 @@ fn a_button_over_a_list_scrolls_the_list_and_still_clicks() {
         events: EventManager::default(),
     };
 
-    // the case in IRIS_TODO.md's report.
+    // A button nested over a scrolling surface must participate in both gestures.
     let list = rsc.ui.widgets.add_strong(Rect::new(PaintId::WHITE));
     let list_weak = list.weak();
     let button = rsc.ui.widgets.add_strong(Rect::new(PaintId::RED));