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.
warning(
        noInstancePropTypes,
        'propTypes was defined as an instance property on %s. Use a static ' +
          'property to define propTypes instead.',
        name,
      );
      const noInstanceContextTypes = !instance.contextTypes;
      warning(
        noInstanceContextTypes,
        'contextTypes was defined as an instance property on %s. Use a static ' +
          'property to define contextTypes instead.',
        name,
      );
      const noComponentShouldUpdate =
        typeof instance.componentShouldUpdate !== 'function';
      warning(
        noComponentShouldUpdate,
        '%s has a method called ' +
          'componentShouldUpdate(). Did you mean shouldComponentUpdate()? ' +
          'The name is phrased as a question because the function is ' +
          'expected to return a value.',
        name,
      );
      if (
        type.prototype &&
        type.prototype.isPureReactComponent &&
        typeof instance.shouldComponentUpdate !== 'undefined'
      ) {
        warning(
          false,