anchor.diff:    State createState() => new ChatScreenState();
   }
   
  -class ChatScreenState extends State<ChatScreen> with TickerProviderStateMixin {
  -  final List<ChatMessage> _messages = <ChatMessage>[];
  +class ChatScreenState extends State<ChatScreen> {
     final TextEditingController _textController = new TextEditingController();
     bool _isComposing = false;
  +
  +  final reference = FirebaseDatabase.instance.reference().child('messages');
   
     Future<Null> _ensureLoggedIn() async {
       GoogleSignInAccount user = googleSignIn.currentUser;
  
positive.code:           children: <Widget>[
              new Container(
                margin: const EdgeInsets.only(right: 16.0),
                child: new GoogleUserCircleAvatar(googleSignIn.currentUser.photoUrl),
              ),
              new Column(
                crossAxisAlignment: CrossAxisAlignment.start,
                children: <Widget>[
                  new Text(googleSignIn.currentUser.displayName,
                      style: Theme.of(context).textTheme.subhead),
                  new Container(
                    margin: const EdgeInsets.only(top: 5.0),
                    child: new Text(text),
                  ),
                ],
              ),
  
negative.code: import 'dart:async';
  import 'package:firebase_analytics/firebase_analytics.dart';
  import 'package:firebase_auth/firebase_auth.dart';
  import 'package:firebase_database/firebase_database.dart';
  import 'package:firebase_database/ui/firebase_animated_list.dart';
  
  final googleSignIn = new GoogleSignIn();
  final analytics = new FirebaseAnalytics();
  