[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).


import {
  getUpdateExpirationTime,
  insertUpdateIntoFiber,
} from './ReactFiberUpdateQueue';
import {createCapturedValue} from './ReactCapturedValue';
import ReactFiberStack from './ReactFiberStack';
const {
  invokeGuardedCallback,
  hasCaughtError,
  clearCaughtError,
} = ReactErrorUtils;
let didWarnAboutStateTransition;
let didWarnSetStateChildContext;
let warnAboutUpdateOnUnmounted;
let warnAboutInvalidUpdates;
if (__DEV__) {
  didWarnAboutStateTransition = false;
  didWarnSetStateChildContext = false;
  const didWarnStateUpdateForUnmountedComponent = {};
  warnAboutUpdateOnUnmounted = function(fiber: Fiber) {
    
    
    const componentName = getComponentName(fiber) || 'ReactClass';
    if (didWarnStateUpdateForUnmountedComponent[componentName]) {
      return;
    }
    warning(
      false,
      "Can't call setState (or forceUpdate) on an unmounted component. This " +
        'is a no-op, but it indicates a memory leak in your application. To ' +