Flutter 如何将WebViewWidget和WillPopScope结合起来

如何将WillPopScope与WebViewWidget结合使用？我只找到了WebView的例子.使用WillPopScope，我需要的是，当按下Back按钮时，它返回到页面https://www.example.com，即Webview的主页.

这是我目前的代码:

import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';

void main() => runApp(MaterialApp(home: WebViewExample()));

class WebViewExample extends StatefulWidget {
  @override
  _WebViewExampleState createState() => _WebViewExampleState();
}

class _WebViewExampleState extends State<WebViewExample> {
  bool showErrorPage = false;

  WebViewController controller = WebViewController();

  @override
  void initState() {
    super.initState();

    controller.setNavigationDelegate(NavigationDelegate(
      onWebResourceError: (WebResourceError error) {
        setState(() {
          showErrorPage = true;
        });
      },
    ));

    controller.setJavaScriptMode(JavaScriptMode.unrestricted);

    controller.loadRequest(Uri.parse("https://www.example.com"));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: showErrorPage 
      ? const Center(
        child: Text('Error!'),
        style: TextStyle(fontSize: 16.0, fontWeight: FontWeight.bold)),
      )
      : WebViewWidget (
        controller: controller,
      )
    );
  }
}