title: tester.scrollUntilVisible() not working with GridView in flutter integration testing
body: <p>I am trying to scroll and find widget from the GridView in <code>integration testing</code> in flutter. But the code not working:</p>
  <pre><code>tester.scrollUntilVisible(itemFinder, -100, scrollable: gridViewFinder)
  </code></pre>
  <p>But this is not working. It is saying GridView is not scrollable.</p>