Don't hardcode the list of events types in fn

sky/examples/fn/widgets/checkbox.dart

 part of widgets;
 
 class Checkbox extends ButtonBase {
 
   bool checked;
   ValueChanged onChanged;
 
   static Style _style = new Style('''
     transform: translateX(0);
     display: flex;
@@ skipping 39 matching lines @@
     border-right-width: 2px;
     border-bottom-width: 2px;
     border-color: #0f9d58;'''
   );
 
   Checkbox({ Object key, this.onChanged, this.checked }) : super(key: key);
 
   Node render() {
     return new Container(
       style: _style,
-      onClick: _handleClick,
-      onPointerDown: _handlePointerDown,
-      onPointerUp: _handlePointerUp,
-      onPointerCancel: _handlePointerCancel,
       children: [
         super.render(),
         new Container(
           style: _highlight ? _containerHighlightStyle : _containerStyle,
           children: [
             new Container(
               style: checked ? _checkedStyle : _uncheckedStyle
             )
           ]
         )
       ]
-    );
+    )..events.listen('click', _handleClick);
   }
 
   void _handleClick(sky.Event e) {
     onChanged(!checked);
   }
 }