(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.
highestPriorityWork = remainingExpirationTime;
          highestPriorityRoot = root;
        }
        if (root === lastScheduledRoot) {
          break;
        }
        previousScheduledRoot = root;
        root = root.nextScheduledRoot;
      }
    }
  }
  
  
  const previousFlushedRoot = nextFlushedRoot;
  if (
    previousFlushedRoot !== null &&
    previousFlushedRoot === highestPriorityRoot &&
    highestPriorityWork === Sync
  ) {
    nestedUpdateCount++;
  } else {
    
    nestedUpdateCount = 0;
  }
  nextFlushedRoot = highestPriorityRoot;
  nextFlushedExpirationTime = highestPriorityWork;
}
function performAsyncWork(dl) {
  performWork(NoWork, dl);