f1828f2971
The whole animation-only traversal thing is quite messy, but it can generally no longer assert that it only deals with already-styled subtrees, since we want to make display animatable. Make it more in line with the regular traversal, in order not to leave the tree in an inconsistent state (an element with display != none that has unstyled children), which the frame constructor complains about (rightfully so). Differential Revision: https://phabricator.services.mozilla.com/D240307