Created attachment 33839 [details] Testcase The attached demo eats about 22% of the CPU, even though only 10 things are animating. I attach a sample; most of it is under AnimationControllerPrivate::updateAnimationTimer(bool), which seems to be firing as fast as it can become some keyframe animation is returning 0 from timeToNextService().
<rdar://problem/7104476>
Created attachment 33840 [details] Patch, changelog
http://trac.webkit.org/changeset/46603
Commit fixed up in r46606