code: function markPercentagesForRecord(record)
          {
              if (!(this._showShortEvents || record.isLong()))
                  return;
              var percentages = this._overviewCalculator.computeBarGraphPercentages(record);
  
              var end = Math.round(percentages.end);
              var categoryName = record.category.name;
              for (var j = Math.round(percentages.start); j <= end; ++j)
                  timelines[categoryName][j] = true;
          }
docs: Create sparse arrays with 101 cells each to fill with chunks for a given category.