title: UIView / can't get corner radius to show when applying gradient
body: <p>The following code creates a square UIView frame with a gradient layer inside a detail view controller.  However, the square.layer.cornerRadius doesn't show.  It remains square. </p>
  
  <pre><code>    class Colors {
      let colorTop = UIColor(red: 68.0/255.0, green: 107.0/255.0, blue: 207.0/255, alpha: 1.0).cgColor
      let colorBottom = UIColor(red: 68.0/255.0, green: 108.0/255.0, blue: 179.0/255, alpha: 1.0).cgColor
  
      let gl: CAGradientLayer
  
      init() {
          gl = CAGradientLayer()
          gl.colors = [ colorTop, colorBottom]
          gl.locations = [ 0.0, 1.0]
       }
     }
  
   class DetailViewController: UIViewController {
  
   func viewWillAppear {
     let colors = Colors() // is a class that creates the gradient
     let square = UIView(frame: CGRect(x: 18, y: 109, width: 60, height: 60))
     square.layer.cornerRadius = 10
     let backgroundLayer = colors.gl
     backgroundLayer.frame = square.frame
     backgroundLayer.maskToBounds = true
     view.layer.insertSublayer(backgroundLayer, at: 1)
    }
   }
  </code></pre>