box(type, definition) {
    const typeCode = shaka.util.Mp4Parser.typeFromString_(type);
    this.headers_.set(typeCode, shaka.util.Mp4Parser.BoxType_.BASIC_BOX);
    this.boxDefinitions_.set(typeCode, definition);
    return this;
  }
Declare a box type as a Box.

@param {string} type
@param {!shaka.util.Mp4Parser.CallbackType} definition
@return {!shaka.util.Mp4Parser}
@export