async addSlides(presentationId, num, predefinedLayout) {
    const requests = [];
    const slideIds = [];
    for (let i = 0; i < num; ++i) {
      slideIds.push(`slide_${i}`);
      requests.push({
        createSlide: {
          objectId: slideIds[i],
          slideLayoutReference: {
            predefinedLayout,
          },
        },
      });
    }
    await this.slidesService.presentations.batchUpdate({
      presentationId,
      resource: {
        requests,
      },
    });
    return slideIds;
  }
Adds slides to a presentation.
@param {string}   presentationId   The presentation ID
@param {number}   num              The number of slides to Add
@param {object}   predefinedLayout The slides' predefined layout
@return {Promise<string[]>} A list of slide ids.