code: function() {
        var timings = {};
        var requests = win.performance.getEntriesByType("resource");
        for (var i = 0; i < requests.length; i++)
          timings[requests[i].name] = requests[i].responseEnd;
        for (var j = 0; j < rects.length; j++) {
          if (!('tm' in rects[j]))
            rects[j].tm = timings[rects[j].url] !== undefined ? timings[rects[j].url] : 0;
        }
      }
docs: Get the time at which each external resource loaded