function setDurationInMillis(duration, startTimeInMillis) {
  this.root.setDurationInMillis(duration, startTimeInMillis)
}
Explicitly set a trace's runtime instead of using it as a stopwatch.
(As a byproduct, stops the timer.)

@param {number} duration Duration of this particular trace.
@param {number} startTimeInMillis (optional) Start of this trace.