anchor.diff:    }
   
     void _measureHeights() {
  -    trace('FixedHeightScrollable::_measureHeights', () {
  -      if (_itemHeight != null)
  -        return;
  -      var root = getRoot();
  -      if (root == null)
  -        return;
  -      var item = root.firstChild.firstChild;
  -      if (item == null)
  -        return;
  -      setState(() {
  -        _height = root.height;
  -        assert(_height > 0);
  -        _itemHeight = item.height;
  -        assert(_itemHeight > 0);
  -        scrollBehavior.containerHeight = _height;
  -        scrollBehavior.contentsHeight = _itemHeight * _itemCount;
  -      });
  +    if (_itemHeight != null)
  +      return;
  +    setState(() {
  +      // TODO(abarth): Actually measure these heights.
  +      _height = 500.0; // root.height;
  +      assert(_height > 0);
  +      _itemHeight = 100.0; // item.height;
  +      assert(_itemHeight > 0);
  +      scrollBehavior.containerHeight = _height;
  +      scrollBehavior.contentsHeight = _itemHeight * _itemCount;
       });
     }
   
  
positive.code:     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).ceil() + 1;
          double alignmentDelta = -scrollOffset % _itemHeight;
  
negative.code:         double drawStart = scrollOffset + alignmentDelta;
          itemNumber = math.max(0, (drawStart / _itemHeight).floor());
  
          transform.translate(0.0, alignmentDelta);
        }
      }
  
      // TODO(abarth): Add a clip.
      return new BlockContainer(
        children: [
          new Transform(
            transform: transform,
            child: new BlockContainer(children: buildItems(itemNumber, drawCount))
          )
        ]
      );
  