title: Trouble downloading files in Google Apps Script web app after Chrome update
body: <p>I've had a Google Apps Script web app running for a bit over a year which gave users an option to download a csv file. It worked perfectly fine, although in the console it gave a warning about downloading from an iFrame being deprecated.</p>
  
  <p>After updating Chrome, I now get the following error when trying to download:</p>
  
  <blockquote>
    <p>Download is disallowed. The frame initiating or instantiating the
    download is sandboxed, but the flag ‘allow-downloads’ is not set. See
    <a href="https://www.chromestatus.com/feature/5706745674465280" rel="noreferrer">https://www.chromestatus.com/feature/5706745674465280</a> for more
    details.</p>
  </blockquote>
  
  <p>When following the above link, it provides the following information:</p>
  
  <blockquote>
    <p>Chrome is planning on removing this capability - i.e. Chrome is going
    to block all downloads initiated from or instantiated in a sandboxed
    iframe by default. The embedder may add "allow-downloads" to the
    sandbox attributes list to opt in. This allows content providers to
    restrict malicious or abusive downloads.</p>
  </blockquote>
  
  <p>How can I add "allow-downloads" to the sandbox attributes in the Google Apps Script environment? Alternatively, is there a workaround to enable downloading files?</p>