 sample for each time
   *    interval with the given type present in the trace. Each sample
   *    represents the total energy used over that time interval.
   *
   * The time intervals are as follows:
   *
   * - "story": The time interval covering the entire user story. There is
   *    always exactly one "story" interval.
   *
   * - "load" : The time interval covered by a page load, from navigationStart
   *    to timeToInteractive. There is one "load" interval for each page load
   *    in the trace.