anchor.diff:          }, ([_]) {
             var viewportHeight = list.offsetHeight;
             var itemsPerViewport = (viewportHeight / rowHeight).floor();
  +          // TODO(jakemac): Update once we resolve
  +          // https://github.com/dart-lang/polymer_interop/issues/6
             list.jsElement.callMethod('pop', ['items']);
             new Future(() {}).then((_) {
               expect(list.items.length, setSize-1);
  
positive.code:           'contribution': 100,
            'target': setSize*rowHeight
          }, ([_]) {
            list.jsElement.callMethod('set', ['items.0.index', phrase]);
            new Future(() {}).then(scrollBackUp);
          });
  
negative.code:       var setSize = 100;
        var phrase = 'It works!';
        list.items = buildDataSet(setSize);
        // TODO(jakemac): Update once we resolve
        // https://github.com/dart-lang/polymer_interop/issues/6
        list.jsElement.callMethod('set', ['items.0.index', phrase]);
        return new Future(() {}).then((_) {
          expect(getFirstItemFromList(list).text, phrase);
  