'Download the given url and add the file to the collection.
Args:
url: The file to download as QUrl.'

def _fetch_url(self, url):

    if (url.scheme() not in ['http', 'https']):
        return
    if (url in self.loaded_urls):
        return
    self.loaded_urls.add(url)
    log.downloads.debug('loading    asset    at    {}'.format(url))
    host_blocker = objreg.get('host-blocker')
    if host_blocker.is_blocked(url):
        log.downloads.debug('Skipping    {},    host-blocked'.format(url))
        self.writer.add_file(urlutils.encoded_url(url), '')
        return
    download_manager = objreg.get('qtnetwork-download-manager', scope='window', window=self._win_id)
    target = downloads.FileObjDownloadTarget(_NoCloseBytesIO())
    item = download_manager.get(url, target=target, auto_remove=True)
    self.pending_downloads.add((url, item))
    item.finished.connect(functools.partial(self._finished, url, item))
    item.error.connect(functools.partial(self._error, url, item))
    item.cancelled.connect(functools.partial(self._cancelled, url, item))
