makeContainer = (properties) => {
      const region = {
        id: '',
        viewportAnchorX: 0,
        viewportAnchorY: 0,
        regionAnchorX: 0,
        regionAnchorY: 0,
        width: 100,
        height: 100,
        widthUnits: shaka.text.CueRegion.units.PERCENTAGE,
        heightUnits: shaka.text.CueRegion.units.PERCENTAGE,
        viewportAnchorUnits: shaka.text.CueRegion.units.PERCENTAGE,
        scroll: '',
      };
      const containerCue = /** @type {!shaka.text.Cue} */ ({
        region,
        nestedCues: jasmine.any(Object),
        payload: '',
        isContainer: true,
      });
      Object.assign(containerCue, properties);
      return mapExpected(containerCue);
    }
@param {!Object} properties
@return {!shaka.text.Cue}