         barButtonItem.width = 18.0
         return barButtonItem
     }()
-    
+
     lazy private var forwardBarButtonItem: UIBarButtonItem = {
         let bundle = NSBundle(forClass: self.classForCoder)
         let image = UIImage(named: "SimpleWebViewController.bundle/forward", inBundle: bundle, compatibleWithTraitCollection: nil)

    lazy var webView: WKWebView = {
        let webView = WKWebView()
        self.view.addSubview(webView)
        
        webView.translatesAutoresizingMaskIntoConstraints = false
        self.view.addConstraints([
            NSLayoutConstraint.init(

        webView.allowsBackForwardNavigationGestures = true
        return webView
    }()

    lazy private var backBarButtonItem: UIBarButtonItem = {
        let bundle = NSBundle(forClass: self.classForCoder)
        let image = UIImage(named: "SimpleWebViewController.bundle/back", inBundle: bundle, compatibleWithTraitCollection: nil)
