Effen: willUmount->didUnmount, allow setState after didUnmount

sky/examples/fn/widgets/fixedheightscrollable.dart

 part of widgets;
 
 abstract class FixedHeightScrollable extends Component {
 
   static Style _style = new Style('''
     overflow: hidden;
     position: relative;
     will-change: transform;'''
   );
 
@@ skipping 46 matching lines @@
           children: items
         )
       ]
     )
     ..events.listen('gestureflingstart', _handleFlingStart)
     ..events.listen('gestureflingcancel', _handleFlingCancel)
     ..events.listen('gesturescrollupdate', _handleScrollUpdate)
     ..events.listen('wheel', _handleWheel);
   }
 
-  void willUnmount() {
+  void didUnmount() {
     _stopFling();
   }
 
   bool _scrollBy(double scrollDelta) {
     var newScrollOffset = _scrollOffset + scrollDelta;
     if (minOffset != null && newScrollOffset < minOffset) {
       newScrollOffset = minOffset;
     } else if (maxOffset != null && newScrollOffset > maxOffset) {
       newScrollOffset = maxOffset;
     }
@@ skipping 40 matching lines @@
   }
 
   void _handleFlingCancel(sky.GestureEvent event) {
     _stopFling();
   }
 
   void _handleWheel(sky.WheelEvent event) {
     _scrollBy(-event.offsetY);
   }
 }