flutter_webview_pluginとwebview_flutterというのがあり、WebviewScaffoldはflutter_webview_pluginのほう。紛らわしい。
@override Widget build(BuildContext context) { return WebviewScaffold( url: "https://flutter.dev/", withJavascript: true, withZoom: false, hidden: true , appBar: AppBar( title: Text("Flutter"), elevation: 1 ), ); }