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`
transaction.rollback(checkpoint);
      this._instance.unstable_handleError(e);
      if (this._pendingStateQueue) {
        this._instance.state = this._processPendingState(
          this._instance.props,
          this._instance.context,
        );
      }
      checkpoint = transaction.checkpoint();
      this._renderedComponent.unmountComponent(
        true ,
        
        true ,
      );
      transaction.rollback(checkpoint);
      
      
      markup = this.performInitialMount(
        renderedElement,
        hostParent,
        hostContainerInfo,
        transaction,
        context,
      );
    }
    return markup;
  },
  performInitialMount: function(
    renderedElement,