Get page source after javascript execution using CefSharp.Offscreen (chromium)

source.cs

private static Task LoadPageAsync(IWebBrowser browser) {
    var tcs = new TaskCompletionSource<bool>();

    void Handler(object sender, LoadingStateChangedEventArgs args) {
        if (args.IsLoading) return;
        browser.LoadingStateChanged -= Handler;
        tcs.TrySetResult(true);
    }

    browser.LoadingStateChanged += Handler;
    return tcs.Task;
}

private static async Task<string> GetPageSourceAsync(string url) {
    using (var browser = new ChromiumWebBrowser(url, new BrowserSettings {
            WindowlessFrameRate = 1 })) {
        await LoadPageAsync(browser);
        return await browser.GetSourceAsync();
    }
}