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`
)
    ) {
      
      
      instance.props = newProps;
      instance.state = newState;
      instance.context = newContext;
      return false;
    }
    
    
    const newInstance = constructClassInstance(workInProgress);
    newInstance.props = newProps;
    newInstance.state = newState = newInstance.state || null;
    newInstance.context = newContext;
    if (typeof newInstance.componentWillMount === 'function') {
      if (__DEV__) {
        startPhaseTimer(workInProgress, 'componentWillMount');
      }
      newInstance.componentWillMount();
      if (__DEV__) {
        stopPhaseTimer();
      }
    }
    
    
    
    const newUpdateQueue = workInProgress.updateQueue;
    if (newUpdateQueue !== null) {
      newInstance.state = beginUpdateQueue(