anchor.diff:        'text': text,
       };
       _firebase.push().set(message);
  -  }
  -
  -  Widget _buildMessage(int index) {
  -    Map<String, String> message = _messages[index];
  -    return new Container(
  -      key: new ValueKey(index),
  -      margin: const EdgeDims.all(3.0),
  -      child: new Center(
  -        child: new Text("${message['name']}: ${message['text']}")
  -      )
  -    );
     }
   
     GlobalKey _messageKey = new GlobalKey();
  
positive.code:     _user = "Guest${new math.Random().nextInt(1000)}";
      _currentMessage = '';
      _firebase.onChildAdded.listen((Event event) {
        Map<String, String> message = event.snapshot.val();
        setState(() => _messages.add(message));
      });
      _messages = <Map<String, String>>[];
      super.initState();
  
negative.code:             new Flexible(
                child: new Block(
                  scrollAnchor: ViewportAnchor.end,
                  children: _messages.map((m) => new ChatMessage(m)).toList()
                )
              ),
              _buildTextComposer(),
  