[This example](https://codesandbox.io/s/1zn2o513pq) presents a huge performance drop between React 16.2 and React 16.3.

In investigated it and noticed several things:

- Perfomance drop is only visible using development bundle
- This is not related to styled-components (a simple div presents the same problem)
- I tried to investigate in performance tab of Chrome dev tools and I noticed that I get React measures even without "?react_perf"
- React Tree Reconciliation seems very long, do not know why

It is not a big problem for me, but it looks weird, so I decided to [share it on Twitter](https://twitter.com/neoziro/status/979756579296817154),  then @gaearon [invited me to submit an issue about it](https://twitter.com/dan_abramov/status/980036013518139398).


const previousIsBatchingUpdates = isBatchingUpdates;
    isBatchingUpdates = true;
    try {
      syncUpdates(fn);
    } finally {
      isBatchingUpdates = previousIsBatchingUpdates;
      if (!isBatchingUpdates && !isRendering) {
        performWork(Sync, false, null);
      }
    }
  }
  return {
    recalculateCurrentTime,
    computeExpirationForFiber,
    scheduleWork,
    requestWork,
    flushRoot,
    batchedUpdates,
    unbatchedUpdates,
    flushSync,
    flushControlled,
    deferredUpdates,
    syncUpdates,
    interactiveUpdates,
    flushInteractiveUpdates,
    computeUniqueAsyncExpiration,
    legacyContext,
  };
}