var nastyGlobalVariable='';
[].forEach
  .call(
    document.querySelectorAll("tr.zA"),
      function(tr) {
        var tit = tr.querySelector(".xW span").getAttribute("title").replace(/at\s+\d+:\d+.*/, '');
        if (tit != nastyGlobalVariable) {
          nastyGlobalVariable = tit;
          tr.insertAdjacentHTML('beforebegin',
            '<tr class=""><td style="width:2px;background:#ccc"></td><td colspan=7 align=center style="background:#ccc;font-size:12px;padding:2px">'
            + tit + '</td></tr>')
        }
      });