docs: function() {
        this.totals = [];
        this.maxTotal = 0;
        this.bounds.reset();
  
        if (this.series_.length === 0)
          return;
  
        var firstSeries = this.series_[0];
        var lastSeries = this.series_[this.series_.length - 1];
  
        this.bounds.addValue(firstSeries.getTimestamp(0));
        this.bounds.addValue(lastSeries.getTimestamp(lastSeries.length - 1));
  
        var numSeries = this.numSeries;
        this.maxTotal = -Infinity;
  
        // Sum the samples at each timestamp.
        // Note, this assumes that all series have all timestamps.
        for (var i = 0; i < firstSeries.length; ++i) {
          var total = 0;
          this.series_.forEach(function(series) {
            total += series.getSample(i).value;
            this.totals.push(total);
          }.bind(this));
  
          this.maxTotal = Math.max(total, this.maxTotal);
        }
      }