title: Flutter Webview change webpage is not available
body: <p>I wanna change the "Webpage not available", in my WebView application, if the user doesn't have internet.</p>
  
  <p>I read the documentation, and try some another puglins</p>
  
  <pre><code>import 'package:webview_flutter/webview_flutter.dart';
  [...]
  class _MyHomePageState extends State&lt;MyHomePage&gt; {
    @override
    Widget build(BuildContext context) {
      return Scaffold(
        body: const WebView(
          initialUrl: 'https://google.com',
          javascriptMode: JavascriptMode.unrestricted,
        ),
      );
    }
  }
  </code></pre>