WebView Fallback not working google sign-in

[alex2844]

When authorizing in the console, the error Scripts may close only the windows that were opened by them

demo: https://github.com/GoogleChrome/android-browser-helper/tree/master/demos/twa-webview-fallback

• os: chrome os 86.0.4217.0
• android-browser-helper 1.3.2

index.html

<b></b>
<button id="authorize_button" style="display: none;">Authorize</button>
<button id="signout_button" style="display: none;">Sign Out</button>
<script type="text/javascript">
	const
		uname = document.querySelector('b'),
		authorizeButton = document.getElementById('authorize_button'),
		signoutButton = document.getElementById('signout_button');
	function handleClientLoad() {
		gapi.load('client:auth2', initClient);
	}
	function initClient() {
		gapi.client.init({
			apiKey: '<YOUR_API_KEY>',
			clientId: '<YOUR_CLIENT_ID>',
			scope: 'email profile'
		}).then(function () {
			gapi.auth2.getAuthInstance().isSignedIn.listen(updateSigninStatus);
			updateSigninStatus();
			authorizeButton.onclick = () => gapi.auth2.getAuthInstance().signIn();
			signoutButton.onclick = () => gapi.auth2.getAuthInstance().signOut();
		}, err => alert(JSON.stringify(err, null, 2)));
	}
	function updateSigninStatus() {
		if (gapi.auth2.getAuthInstance().isSignedIn.get()) {
			const profile = gapi.auth2.getAuthInstance().currentUser.get().getBasicProfile();
			uname.innerText = 'Name: '+profile.getName();
			authorizeButton.style.display = 'none';
			signoutButton.style.display = 'block';
		}else{
			uname.innerText = '';
			authorizeButton.style.display = 'block';
			signoutButton.style.display = 'none';
		}
	}
</script>
<script async defer
	src="https://apis.google.com/js/api.js"
	onload="this.onload=function(){};handleClientLoad()"
	onreadystatechange="if (this.readyState === 'complete') this.onload()"
></script>