constructor({ scaleExtents, documentSize }) {
    this._scaleExtents = scaleExtents;
    this._documentSize = documentSize;
  }
@param {Object} parameters the initialization parameters for this instance.
@param {Extents} parameters.scaleExtents the minimum and maximum allowable scale factor.
@param {Sizee} parameters.documentSize the width and height of the document, in client space.