title: Script message handler not working
body: <p>I am trying to inject a custom WebKit script message handler. My controller is correctly loaded and the view as well. However, on the JS side (from the Safari console), <code>window.webkit.messageHandlers</code> is empty. Any idea why? My app is using iOS 8.1 but even by upgrading to 9.2, it did not work.</p>
  
  <pre><code>import Foundation
  import UIKit
  import WebKit
  
  public class FooController: UIViewController, WKScriptMessageHandler {
      private var wkWebView: WKWebView?
  
      public override func viewDidLoad() {
          super.viewDidLoad()
  
          let o = WKUserContentController()
          o.addScriptMessageHandler(self, name: "foo")
          let config = WKWebViewConfiguration()
          config.userContentController = o
  
          self.wkWebView = WKWebView(frame: self.view.bounds, configuration: config)
          self.view.addSubview(self.wkWebView!)
  
          self.wkWebView!.loadRequest(NSURLRequest(URL: NSBundle.mainBundle().URLForResource("foo", withExtension: "html")!))
      }
  
      public func userContentController(userContentController: WKUserContentController, didReceiveScriptMessage message: WKScriptMessage) {
          print("foo")
      }
  }
  </code></pre>