title: Qt quick controls ListView size issue
body: <p>I have some problem with popup window size behavior using Qt Quick Controls 2. When I'm putting ListView as contentItem for Popup window, Popup window size is zero. Some sample code that reproduce issue:</p>
  
  <pre><code>import QtQuick 2.4
  import QtQuick.Controls 2.0
  import QtQuick.Layouts 1.3
  
  ApplicationWindow {
      id: window
      visible: true
      width: 800
      height: 600
  
      Button {
          text: "open popup"
          onClicked: popup.open()
      }
  
      Popup {
          id: popup
          x: (window.width - width) / 2
          y: window.height / 6
          width: contentWidth
          height: contentHeight
  
          contentItem: ListView {
              width: contentWidth
              height: contentHeight
              model: ListModel {
                  ListElement {
                      name: "Apple"
                      cost: 2.45
                  }
                  ListElement {
                      name: "Orange"
                      cost: 3.25
                  }
                  ListElement {
                      name: "Banana"
                      cost: 1.95
                  }
              }
  
              delegate: RowLayout {
                  Label {
                      text: name
                  }
                  Label {
                      text: cost
                  }
              }
          }
      }
  }
  </code></pre>
  
  <p>How to make popup adopt to the size of ListView?</p>