(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.
workInProgress.actualDuration = 0;
      workInProgress.actualStartTime = 0;
    }
  }
  workInProgress.expirationTime = expirationTime;
  workInProgress.child = current.child;
  workInProgress.memoizedProps = current.memoizedProps;
  workInProgress.memoizedState = current.memoizedState;
  workInProgress.updateQueue = current.updateQueue;
  
  workInProgress.sibling = current.sibling;
  workInProgress.index = current.index;
  workInProgress.ref = current.ref;
  if (enableProfilerTimer) {
    workInProgress.selfBaseTime = current.selfBaseTime;
    workInProgress.treeBaseTime = current.treeBaseTime;
  }
  return workInProgress;
}
export function createHostRootFiber(isAsync: boolean): Fiber {
  let mode = isAsync ? AsyncMode | StrictMode : NoContext;
  if (enableProfilerTimer && isDevToolsPresent) {
    
    
    // 
    mode |= ProfileMode;
  }
  return createFiber(HostRoot, null, null, mode);
}
export function createFiberFromElement(