Note that this patch has a little bit of a belt-and-braces aspect to it.
In each file, either one of the changes should be sufficient, but one of
them prevents us from doing unneeded work and the other one ensures that
we never apply style resulting from transitions and animations even if
somehow we do that work.
Also note that the tests don't actually test anything usefully, since
the reftest harness doesn't currently make the pres context non-dynamic.
(Thus they're marked as failing.) I'm not sure what I should do about
that, though I'm considering just deleting the tests entirely.
