Currently Document::getAnimations doesn't clean style/layout before returning the animations.

This means the following fails:

console.log(document.getAnimations().length); // Say this is currently 0
element.classList.add('animateStyle');
console.log(document.getAnimations().length); // Still returns 0.
window.requestAnimationFrame(function() {
  console.log(document.getAnimations().length); // Now it returns 1.
});

The spec and Firefox immediately have the new animation in document.getAnimations().