title: Twitching scrolling indicator of ListView with dynamic-height items
body: <p>I have a ListView wrapped in Scrollbar. ListView has items with dynamic height.
  The problem is the scrolling indicator twitching on scroll. Here is gif demonstrating the problem (pay attention to the scroll bar on the right):</p>
  <p><a href="https://i.stack.imgur.com/sfLuY.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sfLuY.gif" alt="enter image description here" /></a></p>
  <p>I came to Flutter from iOS where I've been solving such problem by implementing <code>estimatedHeightForRow</code> method of UITableViewDelegate, which allows table (or ListView) to estimate entire height of its dynamic content and show scrolling indicator at the right position.</p>
  <p>Does Flutter have similar solution?</p>
  <p>Here is my code:</p>
  <pre><code>  @override
    Widget build(BuildContext context) {
      super.build(context);
      return Scrollbar(
        child: ListView.separated(
          padding: EdgeInsets.only(top: 16, bottom: 16),
          separatorBuilder: (context, position) =&gt; Divider(),
          itemCount: listViewItems.length,
          itemBuilder: (context, position) {
            final model = listViewItems[position];
            return OrderItemWidget(model: model);
          },
        ),
      );
  </code></pre>