Bug 912033 - Pop down animation keyboard

Fix for [#912033](https://bugzilla.mozilla.org/show_bug.cgi?id=912033). It's dependent on #912028 because of the more sane flow introduced there, plus the tests.

What it does:

1. Don't hide the iframe where the 3rd party keyboard lives until pop down anim is played
2. Change animation to ease-in for pop down because you want slow->fast instead of other way around when disappearing

I tested this on GP Keon with mc and it looks nice and smooth.