code: function filterTabWindows(tabWindows, searchExp) {
    var res;
    if (searchExp === null) {
      res = _.map(tabWindows, function (tw) {
        return new FilteredTabWindow({ tabWindow: tw });
      });
    } else {
      var mappedWindows = _.map(tabWindows, function (tw) {
        return matchTabWindow(tw, searchExp);
      });
      res = _.filter(mappedWindows, function (fw) {
        return fw !== null;
      });
    }
  
    return res;
  }
docs: filter an array of TabWindows using a searchRE to obtain
  an array of FilteredTabWindow