title: Unable to display subview added to WKWebView
body: <p>I am creating an embedded view for an app using Swift and WKWebView. I am stuck in adding and displaying the UIProgressView (my subview).</p>
  
  <p>Whenever I add it on story builder (on top of the view) and then run the app it does not show because of my code (I associate self.view to the instance of WKWebView that I create). </p>
  
  <p><img src="https://i.stack.imgur.com/Y7Oon.png" alt="enter image description here"></p>
  
  <p>I hence tried an <strong>alternative approach</strong> and added it programmatically but won't work either.</p>
  
  <p>Here is my code (for the first approach just ignore the programmatic declaration of UIProgressView):</p>
  
  <pre><code>import UIKit
  import WebKit
  
  class SupportWebView: UIViewController, WKNavigationDelegate {
      @IBOutlet var containerView : UIView? = nil
      @IBOutlet var progressView : UIProgressView? = nil
  
      var webView: WKWebView?
  
      dynamic var myProgress: Double  = 0
      private var myContext = 0
  
      override func loadView() {
          super.loadView()
          self.webView = WKWebView()
          self.view = self.webView
          self.webView?.navigationDelegate = self
          self.webView?.addObserver(self, forKeyPath: "estimatedProgress", options: .New, context: &amp;myContext)
  
          let progressView = UIProgressView(progressViewStyle: .Bar)
          progressView.center = view.center
          progressView.progress = 20.0/30.0
          progressView.trackTintColor = UIColor.lightGrayColor()
          progressView.tintColor = UIColor.blueColor()
          self.webView?.addSubview(progressView)
  //        self.webView.addSubview(progressView)
      }
  </code></pre>
  
  <p>I tried to add the UIProgressView programmatically to the WKWebView view but it won't work.. any suggestion on how to fix this? It seems to display only the main WKWebView and ignore the subviews (they may be rendered before the web view rendering and hence they disappear).</p>