Currently, if you define `shouldComponentUpdate` on `React.PureComponent` nothing bad happens and it acts like `React.Component` https://jsfiddle.net/jekmdfva/

We should probably warn in dev since it defaults the point of `PureComponent`
/**
 * Copyright 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @emails react-core
 */
'use strict';
var React;
var ReactDOM;
describe('ReactPureComponent', () => {
  beforeEach(() => {
    React = require('react');
    ReactDOM = require('react-dom');
  });
  it('should render', () => {
    var renders = 0;
    class Component extends React.PureComponent {
      constructor() {
        super();
        this.state = {type: 'mushrooms'};
      }
      render() {
        renders++;