title: Finds Element without key
body: <p>i'm still new in using flutter driver in testing, but as far as i know there are few identifiers that we can use to locate /  identify elements, like By Text, By Type, etc</p>
  <p>But the problem is, the app that i want to test doesn't have the identifier that i can use to locate them (please correct me if i'm wrong).. the widget code of the app looks like this</p>
  <pre><code>  Widget _buildNextButton() {
      return Align(
        alignment: Alignment.bottomRight,
        child: Container(
          child: IconButton(
            icon: Icon(Icons.arrow_forward),
            onPressed: () =&gt; _controller.nextPage(),
          ),
        ),
      );
    }
  </code></pre>
  <p>where that widget is on a class that extends <code>StatefulWidget</code>.</p>
  <p>How can i locate that icon in my test script and click it? can i use something like this? And what type of finder should i use? (byValueKey? bySemanticLabel? byType? or what?)</p>
  <pre><code>static final arrowKey = find.byValueKey(LoginKey.nextButton);
  TestDriverUtil.tap(driver, arrowKey);
  </code></pre>