anchor.diff:  class _WebViewState extends State<WebView> {
     final Completer<WebViewController> _controller =
         Completer<WebViewController>();
  -
  -  _WebSettings _settings;
   
     @override
     Widget build(BuildContext context) {
  
positive.code: class WebViewController {
    WebViewController._(
      int id,
      this._settings,
      Set<JavascriptChannel> javascriptChannels,
      this._navigationDelegate,
      this._onPageFinished,
    ) : _channel = MethodChannel('plugins.flutter.io/webview_$id') {
      _updateJavascriptChannelsFromSet(javascriptChannels);
      _channel.setMethodCallHandler(_onMethodCall);
    }
  
    final MethodChannel _channel;
  
    NavigationDelegate _navigationDelegate;
  
    _WebSettings _settings;
  
    PageFinishedCallback _onPageFinished;
  
    // Maps a channel name to a channel.
    Map<String, JavascriptChannel> _javascriptChannels =
  
negative.code:         // _navigationDelegate can be null if the widget was rebuilt with no
          // navigation delegate after a navigation happened and just before we
          // got the navigationRequest message.
          final bool allowNavigation = _widget.navigationDelegate == null ||
              _widget.navigationDelegate(request) == NavigationDecision.navigate;
          return allowNavigation;
        case 'onPageFinished':
          if (_widget.onPageFinished != null) {
            _widget.onPageFinished(call.arguments['url']);
          }
  
          return null;
  