[Effen] Use the checkbox widget in the stocks app.

sky/framework/components/fixed_height_scrollable.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import '../animation/scroll_behavior.dart';
 import '../debug/tracing.dart';
 import '../fn.dart';
 import 'dart:math' as math;
 import 'dart:async';
 import 'scrollable.dart';
@@ skipping 59 matching lines @@
     if (_itemHeight == null)
       new Future.microtask(_measureHeights);
 
     if (_height > 0.0 && _itemHeight != null) {
       if (scrollOffset < 0.0) {
         double visibleHeight = _height + scrollOffset;
         drawCount = (visibleHeight / _itemHeight).round() + 1;
         transformStyle =
           'transform: translateY(${(-scrollOffset).toStringAsFixed(2)}px)';
       } else {
-        drawCount = (_height / _itemHeight).round() + 1;
+        drawCount = (_height / _itemHeight).ceil() + 1;
         double alignmentDelta = -scrollOffset % _itemHeight;
         if (alignmentDelta != 0.0)
           alignmentDelta -= _itemHeight;
 
         double drawStart = scrollOffset + alignmentDelta;
         itemNumber = math.max(0, (drawStart / _itemHeight).floor());
 
         transformStyle =
             'transform: translateY(${(alignmentDelta).toStringAsFixed(2)}px)';
       }
     }
 
     return new Container(
       style: _style,
       children: [
         new Container(
           style: _scrollAreaStyle,
           inlineStyle: transformStyle,
           children: buildItems(itemNumber, drawCount)
         )
       ]
     );
   }
 
   List<UINode> buildItems(int start, int count);  
 }