ows the total
  * CPU time spent in |rangeOfInterestCpuTime|, and the list of event labels
  * of the group and their total durations in |rangeOfInterestCpuTime|.
  *
  * Example:
  *   {
  *     layout: {
  *         total: 100,
  *         events: {'FrameView::performPreLayoutTasks': 20,..}},
  *     v8_runtime: {
  *         total: 500,
  *         events: {'String::NewExternalTwoByte': 0.5,..}},
  *     ...
  *   }
  */
  function generateCpuTimeBreakdownTree(mainThread, rangeOfInterest) {
    return ge