webview中的Youtube显示桌面版本的youtube

<iframe width="560" height="315" src="https://www.youtube.com/embed/VIDEO_ID" frameborder="0" allowfullscreen></iframe>

WebView webView = findViewById(R.id.webView);
WebSettings webSettings = webView.getSettings();
webSettings.setUserAgentString("Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3");

let webView = WKWebView(frame: CGRect(x: 0, y: 0, width: 320, height: 480))
webView.customUserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.3"

webView.loadUrl("https://www.youtube.com");

let url = URL(string: "https://www.youtube.com")
let request = URLRequest(url: url!)
webView.load(request)