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.
validateRenderResult(child, Component);
    var childContext;
    if (typeof inst.getChildContext === 'function') {
      var childContextTypes = Component.childContextTypes;
      invariant(
        typeof childContextTypes === 'object',
        '%s.getChildContext(): childContextTypes must be defined in order to ' +
          'use getChildContext().',
        getComponentName(Component) || 'Unknown',
      );
      childContext = inst.getChildContext();
      for (let contextKey in childContext) {
        invariant(
          contextKey in childContextTypes,
          '%s.getChildContext(): key "%s" is not defined in childContextTypes.',
          getComponentName(Component) || 'Unknown',
          contextKey,
        );
      }
    }
    if (childContext) {
      context = Object.assign({}, context, childContext);
    }
  }
  return {child, context};
}
type Frame = {
  domNamespace: string,
  children: FlatReactChildren,
  childIndex: number,