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`
}
      } else {
        if (__DEV__) {
          measureLifeCyclePerf(
            () => inst.componentWillUnmount(),
            this._debugID,
            'componentWillUnmount',
          );
        } else {
          inst.componentWillUnmount();
        }
      }
    }
    if (this._renderedComponent) {
      ReactReconciler.unmountComponent(
        this._renderedComponent,
        safely,
        skipLifecycle,
      );
      this._renderedNodeType = null;
      this._renderedComponent = null;
      this._instance = null;
    }
    
    
    
    this._pendingStateQueue = null;
    this._pendingReplaceState = false;
    this._pendingForceUpdate = false;
    this._pendingCallbacks = null;