valuePositionToAngle_(valuePct) {
    const startAngle = googMath.standardAngle((360 - this.angleSpan_) / 2 + 90);
    return this.angleSpan_ * valuePct + startAngle;
  }
Convert a value-position (percent in the range) to an angle based on
the angle span. A value-position is a value that has been proportinally
adjusted to a value betwwen 0-1, proportionaly to the range.
@param {number} valuePct The value.
@return {number} The angle where this value is located on the round
    axis, based on the range and angle span.
@private