constructor(player) {
    this.player = player;
    this.thumbnails = [];
    this.loaded = false;
    this.lastMouseMoveTime = Date.now();
    this.mouseDown = false;
    this.loadedImages = [];

    this.elements = {
      thumb: {},
      scrubbing: {},
    };

    this.load();
  }
PreviewThumbnails constructor.
@param {Plyr} player
@return {PreviewThumbnails}