有没有办法在关闭运行flutter应用程序的浏览器选项卡时显示警告对话框？

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Webview Demo',
      home: Scaffold(
        appBar: AppBar(
          title: Text('Flutter Webview Demo'),
        ),
        body: WebView(
          initialUrl: 'https://example.com',
          javascriptMode: JavascriptMode.unrestricted,
          onPageFinished: (String url) {
            // 注册beforeunload事件处理函数
            js.context['beforeunload'] = js.allowInterop((_) {
              // 显示警告对话框
              return '您确定要关闭此应用吗？';
            });
          },
        ),
      ),
    );
  }
}

void main() => runApp(MyApp());

dependencies:
  flutter:
    sdk: flutter
  webview_flutter: ^2.0.12
  js: ^0.6.2