s.appendChild(selectEl);

    getAsync('/tracing/test_data/__file_list__', function(data) {
      const files = JSON.parse(data);
      for (let i = 0; i < files.length; ++i) {
        const opt = document.createElement('option');
        opt.value = files[i];
        opt.textContent = cleanFilename(files[i]);
        selectEl.appendChild(opt);
      }
      selectEl.selectedIndex = 0;
      selectEl.onchange = onSelectionChange;

      if (!window.location.hash) {
        // This will trigger an onHashChan