title: Flutter icons do not show
body: <p>I am trying to complete <a href="https://codelabs.developers.google.com/codelabs/first-flutter-app-pt2/#3" rel="noreferrer">this</a> Flutter Code Lab, but the icons do not appear in my application. But they appears in Android Studio code:<a href="https://i.stack.imgur.com/WYrtm.png" rel="noreferrer"><img src="https://i.stack.imgur.com/WYrtm.png" alt="enter image description here"></a>
  I have been included the lib in my file <code>pubspec.yaml</code></p>
  
  <pre><code>name: startup_namer
  description: A new Flutter application.
  
  dependencies:
    flutter:
      sdk: flutter
  
    cupertino_icons: ^0.1.0
    english_words: ^3.1.0
  </code></pre>
  
  <p>But result is this:<a href="https://i.stack.imgur.com/2sovX.png" rel="noreferrer"><img src="https://i.stack.imgur.com/2sovX.png" alt="enter image description here"></a></p>
  
  <p>My main.dart file looks like this:</p>
  
  <pre><code>// Add the heart icons to the ListView.
  
  import 'package:flutter/material.dart';
  import 'package:english_words/english_words.dart';
  
  
  void main() =&gt; runApp(new MyApp());
  
  class MyApp extends StatelessWidget {
  
     ..... 
  
    Widget _buildRow(WordPair pair) {
      final bool alreadySaved = _saved.contains(pair);
  
      return new ListTile(
        title: new Text(
          pair.asPascalCase,
          style: _biggerFont,
        ),
        trailing: new Icon(
          alreadySaved ? Icons.favorite : Icons.favorite_border,
          color: alreadySaved ? Colors.red : null,
          size: 22.0,
        ),
        onTap: () {      
          setState(() {
            if (alreadySaved) {
              _saved.remove(pair);
            } else {
              _saved.add(pair);
            }
          });
        },
      );
    }
  }
  </code></pre>
  
  <p>I thought that is because I use iOS emulator, but when I tried with Android emulator the result was the same.</p>