addAndMarkChip_(markChipBad) {
    this.addChip();

    if (markChipBad) {
      var chip = this.getChildAt(this.getChildCount() - 1);
      goog.dom.classlist.add(chip.getElement(), constants.CssClass.BAD_CHIP);
    }
  }
Adds a chip and marks it as bad if needed.
@param {boolean} markChipBad Whether to mark the chip bad.
@private