Follow up from https://github.com/facebook/react/pull/11616.

Here's one I found. These two invariants:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L330-L343

are in a function that's behind a DEV block:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L447-L449

I don't think this is intentional, but need to verify.

There may be more. I'll use this issue to track while https://github.com/facebook/react/pull/11616 preserves existing behavior.
Object.defineProperty(fakeInternalInstance, '_processChildContext', {
    enumerable: false,
    value: function() {
      invariant(
        false,
        '_processChildContext is not available in React 16+. This likely ' +
          'means you have multiple copies of React and are attempting to nest ' +
          'a React 15 tree inside a React 16 tree using ' +
          "unstable_renderSubtreeIntoContainer, which isn't supported. Try " +
          'to make sure you have only one copy of React (and ideally, switch ' +
          'to ReactDOM.createPortal).',
      );
    },
  });
  Object.freeze(fakeInternalInstance);
}
export default function(
  scheduleWork: (fiber: Fiber, expirationTime: ExpirationTime) => void,
  computeExpirationForFiber: (fiber: Fiber) => ExpirationTime,
  memoizeProps: (workInProgress: Fiber, props: any) => void,
  memoizeState: (workInProgress: Fiber, state: any) => void,
) {
  
  const updater = {
    isMounted,
    enqueueSetState(instance, partialState, callback) {