title: After Chrome version 83 release, file download in modal dialog doesn't work
body: <p>I use Google Apps Script to make download Spreadsheet data quickly.</p>
  
  <p>Since several days before, download function doesn't work suddenly.
  Some of my coworkers who can use the function use chrome version 81.0.4044.138（Official Build）
  and who cannot use the function , chrome version 83.0.4103.61（Official Build）</p>
  
  <p>(right-click and [save as] works fortunately)</p>
  
  <p>I want to know what should I do to make one-click download function active again.</p>
  
  <p>Script is as follows.</p>
  
  <pre><code>/**
   * Adds a custom menu
   *
   * @param {Object} e The event parameter for a simple onOpen trigger.
   */
  function onOpen(e) {
    SpreadsheetApp.getUi()
        .createMenu('Custom')
        .addItem('Download as XLSX', 'downloadXLS_GUI')
        .addToUi();
  }
  
  
  /**
   * Display a modal dialog with a single download link.
   *
   * From: http://stackoverflow.com/a/37336778/1677912
   */
  function downloadXLS_GUI() {
    // Get current spreadsheet's ID, place in download URL
    var ssID = SpreadsheetApp.getActive().getId();
    var URL = 'https://docs.google.com/spreadsheets/d/'+ssID+'/export?format=xlsx';
  
    // Display a modal dialog box with download link.
    var htmlOutput = HtmlService
                    .createHtmlOutput('&lt;a href="'+URL+'"&gt;Click to download&lt;/a&gt;')
                    .setSandboxMode(HtmlService.SandboxMode.IFRAME)
                    .setWidth(800)
                    .setHeight(600);
    SpreadsheetApp.getUi().showModalDialog(htmlOutput, 'Download XLS');
  }
  
  </code></pre>