(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.
next.effectTag &= HostEffectMask;
        return next;
      }
      if (returnFiber !== null) {
        
        returnFiber.firstEffect = returnFiber.lastEffect = null;
        returnFiber.effectTag |= Incomplete;
      }
      if (__DEV__ && ReactFiberInstrumentation.debugTool) {
        ReactFiberInstrumentation.debugTool.onCompleteWork(workInProgress);
      }
      if (siblingFiber !== null) {
        
        return siblingFiber;
      } else if (returnFiber !== null) {
        
        workInProgress = returnFiber;
        continue;
      } else {
        return null;
      }
    }
  }
  
  
  
  return null;
}
function performUnitOfWork(workInProgress: Fiber): Fiber | null {