(Regarding the experimental `React.unstable_Profiler` API and reactjs/rfcs/pull/51.)

PR #13058 changed the behavior of React profiling builds to opt host roots into `ProfileMode` if the React DevTools extension is detected. This was necessary in order to have accurate tree base time measurements for the visual flame graphs.

The Profiler plug-in for DevTools does feature detection to determine if it's enabled by looking at each root and seeing if any of the fibers contain an `actualDuration` attribute,

The problem is that the `actualDuration` attribute will be present on v16.4 fibers, which pre-date PR #13058. As a result, the Profiler UI may enable itself with versions of React that it cannot work correctly with.

Perhaps an easy solution would be to rename one of the `unstable_Profiler`'s fiber attributes prior to the next minor release (e.g. `treeBaseTime` -> `treeBaseDuration`) and change the DevTools Profiler to feature check using this new name instead.
}
function performSyncWork() {
  performWork(Sync, null);
}
function performWork(minExpirationTime: ExpirationTime, dl: Deadline | null) {
  deadline = dl;
  
  
  findHighestPriorityRoot();
  if (enableProfilerTimer) {
    resumeActualRenderTimerIfPaused(minExpirationTime === Sync);
  }
  if (deadline !== null) {
    recomputeCurrentRendererTime();
    currentSchedulerTime = currentRendererTime;
    if (enableUserTimingAPI) {
      const didExpire = nextFlushedExpirationTime < currentRendererTime;
      const timeout = expirationTimeToMs(nextFlushedExpirationTime);
      stopRequestCallbackTimer(didExpire, timeout);
    }
    while (
      nextFlushedRoot !== null &&
      nextFlushedExpirationTime !== NoWork &&
      (minExpirationTime === NoWork ||
        minExpirationTime >= nextFlushedExpirationTime) &&
      (!deadlineDidExpire || currentRendererTime >= nextFlushedExpirationTime)
    ) {
      performWorkOnRoot(
        nextFlushedRoot,
        nextFlushedExpirationTime,