5487b95472
Having UniqueComponent automatically generate its own key is a trap. If anyone ever creates a UniqueComponent in a build function (rather than ahead of time) and forgets to pass a key, then that entire subtree is going to be rebuilt, including layout, every time it's updated. Since there's basically no way for us to catch this, we should at least force the author to see the explicit "new GlobalKey()" call in their code.