Created attachment 33839 [details]
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().
Created attachment 33840 [details]
Commit fixed up in r46606