Deflake transitions/hang-with-bad-transition-list.html.

Turns out to just be a race in the test. The first rAF callback
is getting called after the animation has finished and the sync
checkRunning call was before the animation started.

BUG=303314

Review URL: https://codereview.chromium.org/25807002

git-svn-id: svn://svn.chromium.org/blink/trunk@158830 bbb929c8-8fbe-4397-9dbb-9b2b20218538