barGraph(stats = this.stats) {
    // const MAX_TERMINAL_CHARS = process.stdout.columns;
    const maxBarWidth = 30;

    const jsSegment = ' '.repeat((stats.jsUsed / stats.totalBytes) * maxBarWidth);
    const cssSegment = ' '.repeat((stats.cssUsed / stats.totalBytes) * maxBarWidth);
    const unusedSegment = ' '.repeat(maxBarWidth - jsSegment.length - cssSegment.length);

    return chalk.bgRedBright(jsSegment) + chalk.bgBlueBright(cssSegment) +
           chalk.bgBlackBright(unusedSegment);
  }
Constructors a bar chart for the % usage of each value.
@param {!{jsUsed: number, cssUsed: number, totalBytes: number}=} stats Usage stats.
@return {string}