Initializing a google map on on-core-animated-pages-transition-prepare callback causes slide-from-right to fail

[livtanong]

But this effect only happens going forward. The transition works correctly moving backwards, presumably because the google map already exists and doesn't need initialization. hero, cross-fade, and slide-up transitions are unaffected.

Also, in case anyone is wondering why the google map init has to happen during the callback, see #10.

Applying the map init on core-animated-pages-transition-end works.
Applying the map init on a timeout for core-animated-pages-transition-prepare also works.

[ebidel]

In fact, doing any JS worked in a core-animated-pages-transition-prepare handler causes the forward transition to fail. Here's another example: http://jsbin.com/hibeda/1/edit