Input nodes leaked by the browser retain React fibers

**Do you want to request a *feature* or report a *bug*?** 🐛 **What is the current behavior?** Browsers retain references to inputs in their undo stacks, which in turn retain React fibers (including `memoizedProps`) See https://bugs.chromium.org/p/chromium/issues/detail?id=1029189 **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:** https://jsfiddle.net/altxg/nzu6ab5e/3/ **What is the expected behavior?** Although the leak originates from the browser, it might be helpful if React detached internal fiber references from input and contenteditable nodes on unmount **Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?** All versions of React as far as I know. I can reproduce the leak on Chrome and Firefox on Mac --- Potentially related issues: https://github.com/facebook/react/issues/12692 https://github.com/facebook/react/issues/16087