code: function TimerEvent(label, color, pause, thread_id) {
      assert(thread_id >= 0 && thread_id < kNumThreads, "invalid thread id");
      this.label = label;
      this.color = color;
      this.pause = pause;
      this.ranges = [];
      this.thread_id = thread_id;
      this.index = ++num_timer_event;
    }
docs: Data structures.