Determine if user has enabled application's Safari content blocker extension

I'm working on a Safari Content Blocking extension. I intend to show setup instructions if the extension is disabled and to show settings if it is conversely enabled. How can I determine if the extension is enabled by the user?

I've seen this method to detect if a custom keyboard is activated but there's no key on NSUserDefaults that relates to Safari Content Blockers.

As of iOS 10, there is a new method in SFContentBlockerManager to support this:

getStateOfContentBlocker(withIdentifier:completionHandler:)

And you call it like this (Swift 3):

SFContentBlockerManager.getStateOfContentBlocker(withIdentifier: "your.identifier.here", completionHandler: { (state, error) in
    if let error = error {
        // TODO: handle the error
    }
    if let state = state {
        let contentBlockerIsEnabled = state.isEnabled
        // TODO: do something with this value
    }
})