Ideally, I'd prefer to keep the veiled/unveiled classes on topUi, AND add `#splashScreen.veiled`/`#splashScreen.unveiled` on top of that. The reason is that Polymer's promise is to automate veiling/unveiling at precisely the right moment - it seems not to live up to that right now, but hopefully this will get fixed. If we leave those hooks in, it will be easier to switch later. But it's not a deal breaker - feels free to merge.