Detect if browser (IWebDriver) supports taking screenshots

I'm spiking out using BrowserStack and it looks like the RemoteWebDriver does not support ITakesScreenshot by default. They have a way of working around it but I am guessing others will fall into this sort of problem.

Now I am not sure if my solution is the best. I am returning an empty byte array when screenshots are not supported. I'm guessing returning Some(byte[]) would be a more F# way of doing this. 

Thoughts?