title: Flutter appBar Backbutton doesn't appear
body: <p>I've successfully navigated to a class in a new file, but now I'm not getting a backbutton on my appBar.  Here is my navigation from main.dart...</p>
  
  <pre><code>new RaisedButton(
                  onPressed: () {
                    Navigator.pushNamed(context, '/searchpage');
                  },
  </code></pre>
  
  <p>and here is my SearchPage appBar..</p>
  
  <pre><code>class SearchPageState extends State&lt;SearchPage&gt; {
    @override
    Widget build(BuildContext context) {
      return new MaterialApp(
          routes: &lt;String, WidgetBuilder&gt;{
            '/loginpage': (BuildContext context) =&gt; new Login.LoginPage(),
            '/mainpage': (BuildContext context) =&gt; new Main.MyApp(),
          },
          home: new Scaffold(
        appBar: new AppBar(
          title: new Text(
            "Search",
            style: new TextStyle(fontWeight: FontWeight.bold),
          ),
        ),
  </code></pre>