How to quit a full screen web app

We are trying to get our web app to run as a full screen web app. I got this to work using these meta tags:

    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="apple-mobile-web-app-status-bar-style" content="default">
    <meta name="apple-mobile-web-app-title" content="Full Screen">

So now when you launch the web app from your home screen on iPhone or android devices, it will launch into full screen (with no browser controls).

Now we need a way to allow the user to quit, I was hoping to create a menu that had a quit button but using window.close() gives me the following error in chrome:

Scripts may close only the windows that were opened by it.

What would be the correct way to handle this?