(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.
}
  if (isBatchingUpdates) {
    
    if (isUnbatchingUpdates) {
      
      
      nextFlushedRoot = root;
      nextFlushedExpirationTime = Sync;
      performWorkOnRoot(root, Sync, true);
    }
    return;
  }
  
  if (expirationTime === Sync) {
    performSyncWork();
  } else {
    scheduleCallbackWithExpirationTime(expirationTime);
  }
}
function addRootToSchedule(root: FiberRoot, expirationTime: ExpirationTime) {
  
  
  if (root.nextScheduledRoot === null) {
    
    root.expirationTime = expirationTime;
    if (lastScheduledRoot === null) {
      firstScheduledRoot = lastScheduledRoot = root;
      root.nextScheduledRoot = root;
    } else {
      lastScheduledRoot.nextScheduledRoot = root;