初始化

<!--浏览器-->
<cefSharpWPF:ChromiumWebBrowser Name="webBrowser" 
                                Grid.Row="0" >
</cefSharpWPF:ChromiumWebBrowser>

public MainWindow()
{
    InitializeComponent();

    //右键菜单栏
    MenuHandler.mainWindow = this;
    webBrowser.MenuHandler = new MenuHandler();
}

MenuHandler.cs

public class MenuHandler : IContextMenuHandler
{
    public static Window mainWindow { get; set; }
    void IContextMenuHandler.OnBeforeContextMenu(IWebBrowser browserControl, IBrowser browser, IFrame frame, IContextMenuParams parameters, IMenuModel model)
    {

    }

    bool IContextMenuHandler.OnContextMenuCommand(IWebBrowser browserControl, IBrowser browser, IFrame frame, IContextMenuParams parameters, CefMenuCommand commandId, CefEventFlags eventFlags)
    {
        return true;
    }

    void IContextMenuHandler.OnContextMenuDismissed(IWebBrowser browserControl, IBrowser browser, IFrame frame)
    {
        //隐藏菜单栏
        var chromiumWebBrowser = (ChromiumWebBrowser)browserControl;

        chromiumWebBrowser.Dispatcher.Invoke(() =>
        {
            chromiumWebBrowser.ContextMenu = null;
        });
    }

    bool IContextMenuHandler.RunContextMenu(IWebBrowser browserControl, IBrowser browser, IFrame frame, IContextMenuParams parameters, IMenuModel model, IRunContextMenuCallback callback)
    {

        //绘制了一遍菜单栏  所以初始化的时候不必绘制菜单栏，再此处绘制即可
        var chromiumWebBrowser = (ChromiumWebBrowser)browserControl;

        chromiumWebBrowser.Dispatcher.Invoke(() =>
        {
            var menu = new ContextMenu
            {
                IsOpen = true
            };

            RoutedEventHandler handler = null;

            handler = (s, e) =>
            {
                menu.Closed -= handler;

                //If the callback has been disposed then it's already been executed
                //so don't call Cancel
                if (!callback.IsDisposed)
                {
                    callback.Cancel();
                }
            };

            menu.Closed += handler;

            menu.Items.Add(new MenuItem
            {
                Header = "最小化",
                Command = new CustomCommand(MinWindow)
            });
            menu.Items.Add(new MenuItem
            {
                Header = "关闭",
                Command = new CustomCommand(CloseWindow)
            });
            chromiumWebBrowser.ContextMenu = menu;

        });

        return true;
    }

    /// <summary>
    /// 关闭窗体
    /// </summary>
    private void CloseWindow()
    {
        //调用线程无法访问此对象,因为另一个线程拥有该对象
        //handler和window是两个线程，WPF做了线程安全。。。so以下
        mainWindow.Dispatcher.Invoke(
            new Action(
                    delegate
                    {
                        Application.Current.Shutdown();
                    }
                ));
    }

    /// <summary>
    /// 最小化窗体
    /// </summary>
    private void MinWindow()
    {
        mainWindow.Dispatcher.Invoke(
            new Action(
                    delegate
                    {
                        mainWindow.WindowState = WindowState.Minimized;
                    }
                ));
    }

    private static IEnumerable<Tuple<string, CefMenuCommand>> GetMenuItems(IMenuModel model)
    {
        var list = new List<Tuple<string, CefMenuCommand>>();
        for (var i = 0; i < model.Count; i++)
        {
            var header = model.GetLabelAt(i);
            var commandId = model.GetCommandIdAt(i);
            list.Add(new Tuple<string, CefMenuCommand>(header, commandId));
        }

        return list;
    }
}

CustomCommand.cs

public class CustomCommand : ICommand
{
    Action _TargetExecuteMethod;
    Func<bool> _TargetCanExecuteMethod;
    public event EventHandler CanExecuteChanged = delegate { };

    public CustomCommand(Action executeMethod)
    {
        _TargetExecuteMethod = executeMethod;
    }

    bool ICommand.CanExecute(object parameter)
    {
        if (_TargetCanExecuteMethod != null)
        {
            return _TargetCanExecuteMethod();
        }
        if (_TargetExecuteMethod != null)
        {
            return true;
        }
        return false;
    }

    public void RaiseCanExecuteChanged()
    {
        CanExecuteChanged(this, EventArgs.Empty);
    }

    void ICommand.Execute(object parameter)
    {
        _TargetExecuteMethod?.Invoke();
    }
}

参考资料

https://github.com/cefsharp/CefSharp/issues/1795