nextContext arg in shouldComponentUpdate() method

<!-- Note: if the issue is about documentation or the website, please file it at: https://github.com/reactjs/reactjs.org/issues/new --> **Do you want to request a *feature* or report a *bug*?** I think it is feature, but could be a bug also **What is the current behavior?** When I subscribe to context using React16.6.0 contextType API, component rerenders even when unused context properties was changed. So, I want to use shouldComponentUpdate(), but that method don't have nextContext argument. Is there any other way to solve this problem? **If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem. Your bug will get fixed much faster if we can run your code and it doesn't have dependencies other than React. Paste the link to your JSFiddle (https://jsfiddle.net/Luktwrdm/) or CodeSandbox (https://codesandbox.io/s/new) example below:** **What is the expected behavior?** **Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**