title: How to popup a file dialog/print dialog in a html file that is rendered in a WebEngineView?
body: <p>I have a local html file that use highcharts to display my data and save to images, it works well in chrome browser, then I try to load it in Qt 5.9.4 with a WebEngineView (QML type),  all the popup dialogs are unable to dispaly.</p>
  
  <p>html file code: <a href="https://jsfiddle.net/sylaince/9x9j5Lpj/" rel="nofollow noreferrer">https://jsfiddle.net/sylaince/9x9j5Lpj/</a></p>
  
  <pre><code>&lt;div id="container" style="width: 100%; min-height: 400px"&gt;&lt;/div&gt;
  &lt;script src="https://code.highcharts.com/highcharts.js"&gt;&lt;/script&gt;
  &lt;script src="https://code.highcharts.com/modules/exporting.js"&gt;&lt;/script&gt;
  &lt;script src="https://code.highcharts.com/modules/offline-exporting.js"&gt;&lt;/script&gt;
  &lt;script src="https://code.highcharts.com/modules/export-data.js"&gt;&lt;/script&gt;
  &lt;script type="text/javascript"&gt;
      Highcharts.setOptions({
          navigation: {
              menuItemStyle: {
                  padding: '6px 14px'
              }
          }
      });
      var chart = new Highcharts.Chart({
          chart: {
              renderTo: 'container'
          },
          exporting: {
              filename: 'data'
          },
          title: {
              text: 'export file'
          },
          xAxis: {
              categories: ['1', '2', '3', '4', '5', '6', '7', '8', '9', '10', '11', '12']
          },
          series: [{
              name: 'test data',
              data: [29.9, 71.5, 106.4, 129.2, 144.0, 176.0, 135.6, 148.5, 216.4, 194.1, 95.6, 54.4]
          }]
      });
  &lt;/script&gt;
  </code></pre>
  
  <p>qml file:</p>
  
  <pre><code>Page {  
      WebEngineView {
          id: webView
          anchors.fill: parent
          url: "qrc:/html/index.html"
      }
  }
  </code></pre>
  
  <p>How to make WebEngineView to show dialog such as file dialog, print dialog, etc.</p>