**Do you want to request a *feature* or report a *bug*?**
bug

**What is the current behavior?**
In normal rendering, you can memoize a class-based component: https://jsfiddle.net/586ea3cx/

With the shallow renderer, it seems like you can't: https://jsfiddle.net/odj217Lv/1/

This might be blocking https://github.com/airbnb/enzyme/pull/1914, in which tests are failing with `Cannot call a class as a function`. (it's tough to repro stuff with the shallow renderer)
import type {ReactElement} from 'shared/ReactElementType';
type BasicStateAction<S> = (S => S) | S;
type Dispatch<A> = A => void;
type Update<A> = {
  action: A,
  next: Update<A> | null,
};
type UpdateQueue<A> = {
  last: Update<A> | null,
  dispatch: any,
};
type Hook = {
  memoizedState: any,
  queue: UpdateQueue<any> | null,
  next: Hook | null,
};
const {ReactCurrentDispatcher} = ReactSharedInternals;
const RE_RENDER_LIMIT = 25;
const emptyObject = {};
if (__DEV__) {
  Object.freeze(emptyObject);
}
let currentHookNameInDev: ?string;
function areHookInputsEqual(
  nextDeps: Array<mixed>,
  prevDeps: Array<mixed> | null,
) {
  if (prevDeps === null) {
    warning(
      false,