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`
if (this._pendingStateQueue) {
        inst.state = this._processPendingState(inst.props, inst.context);
      }
    }
    var markup;
    if (inst.unstable_handleError) {
      markup = this.performInitialMountWithErrorHandling(
        renderedElement,
        hostParent,
        hostContainerInfo,
        transaction,
        context,
      );
    } else {
      markup = this.performInitialMount(
        renderedElement,
        hostParent,
        hostContainerInfo,
        transaction,
        context,
      );
    }
    if (inst.componentDidMount) {
      if (__DEV__) {
        transaction.getReactMountReady().enqueue(() => {
          measureLifeCyclePerf(
            () => inst.componentDidMount(),
            this._debugID,
            'componentDidMount',
          );