code: function profileBlock(block, repeat){
    repeat = repeat || DEFAULT_REPEAT_COUNT;
    let start = process.hrtime();
    for (let i = 0; i < repeat; ++i){
      block();
    }
    let diff = process.hrtime(start);
    return Math.floor(diff[0] + diff[1] / 1e3);
  }
docs: Profile code block.
  @param {function} block - code to run.
  @param {Number} [repeat] - Number of repeated times
  @returns {Number} Total running time in microseconds.