(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 (typeof currentRef === 'function') {
      currentRef(null);
    } else {
      currentRef.current = null;
    }
  }
}
function commitUnmount(current: Fiber): void {
  if (typeof onCommitUnmount === 'function') {
    onCommitUnmount(current);
  }
  switch (current.tag) {
    case ClassComponent: {
      safelyDetachRef(current);
      const instance = current.stateNode;
      if (typeof instance.componentWillUnmount === 'function') {
        safelyCallComponentWillUnmount(current, instance);
      }
      return;
    }
    case HostComponent: {
      safelyDetachRef(current);
      return;
    }
    case HostPortal: {
      
      
      
      if (supportsMutation) {
        unmountHostComponents(current);