get _effectiveStep() {
      let step = this.step;
      if (step < 0) {
        step = Math.abs(step);
      }
      if (Number.isNaN(step)) {
        step = 1;
      }
      return step;
    }
Normalizes a new <code>step</code> property value.
If tickmarks are enabled recreates them according to it.

@private