function SpecularEnvironmentCubeMap(url) {
  this._url = url;

  this._cubeMapBuffers = undefined;
  this._texture = undefined;

  this._maximumMipmapLevel = undefined;

  this._loading = false;
  this._ready = false;

  this._errorEvent = new Event();
}
Manages a cube map for use as a specular environment map.

@alias SpecularEnvironmentCubeMap
@constructor

@param {string} url The url to the KTX2 file containing the specular environment map and convoluted mipmaps.
@private