如何在Flutter web应用中进入全屏模式

dependencies:
  flutter:
    sdk: flutter
  webview_flutter: ^2.0.0

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

class FullScreenWebView extends StatefulWidget {
  @override
  _FullScreenWebViewState createState() => _FullScreenWebViewState();
}

class _FullScreenWebViewState extends State<FullScreenWebView> {
  final Completer<WebViewController> _controller =
      Completer<WebViewController>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: WebView(
        initialUrl: 'https://example.com',
        javascriptMode: JavascriptMode.unrestricted,
        onWebViewCreated: (WebViewController webViewController) {
          _controller.complete(webViewController);
        },
      ),
    );
  }
}

class _FullScreenWebViewState extends State<FullScreenWebView> {
  final Completer<WebViewController> _controller =
      Completer<WebViewController>();
  bool _isFullScreen = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: [
          WebView(
            initialUrl: 'https://example.com',
            javascriptMode: JavascriptMode.unrestricted,
            onWebViewCreated: (WebViewController webViewController) {
              _controller.complete(webViewController);
            },
          ),
          Positioned(
            top: 20,
            right: 20,
            child: FloatingActionButton(
              onPressed: () {
                setState(() {
                  _isFullScreen = !_isFullScreen;
                });
                _controller.future.then((controller) {
                  controller?.evaluateJavascript(
                      'document.documentElement.requestFullscreen();');
                });
              },
              child: Icon(_isFullScreen ? Icons.fullscreen_exit : Icons.fullscreen),
            ),
          ),
        ],
      ),
    );
  }
}