title: flutter drawer Hamburger icon is not showing when i chance Directionality
body: <p>I am trying to make my app RTL and I want the drawer to be on the right side. I managed to open it from the right direction but the hamburger menu icon disappeared.</p>
  
  <p>This is code to make the layout <code>rtl</code>:</p>
  
  <pre><code>class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      return new MaterialApp(
        title: 'Flutter task',
        home: Directionality(
          textDirection: TextDirection.rtl,
            child: new MyHomePage()
        ),
      );
    }
  }`
  </code></pre>
  
  <p>and this is my drawer :</p>
  
  <pre><code>              drawer: new Container(
              constraints: new BoxConstraints.expand(
                width: MediaQuery
                    .of(context)
                    .size
                    .width - 60,
              ),
              color: Colors.black.withOpacity(0.6),
              alignment: Alignment.center,
                child: new ListView(
                 children: &lt;Widget&gt;[
                   Text('1'),
                   Text('2')
                 ],
                ),
  
            ),
  </code></pre>
  
  <p>What am I missing?</p>