Hover over the text and move the mouse around a bit, then move it off the window so that no more transitions are happening. Note that the CPU usage doesn't go back down.
Created attachment 25822 [details]
reduced testcase formerly on remote site
Created attachment 26402 [details]
Somewhat smaller testcase
Created attachment 26403 [details]
The Shark trace show that almost all the time is in AnimationController code. There's a lot of animation thrash going on here.
This is not a case of "0 duration animation" as in the bug it is duped on. But the animation time is very short (0.15s) and there are tons of animations firing at once. So it takes longer than the duration to process them all, and it was hitting the same case where the animation time stopped updating before the animation finished. All fixed now.
*** This bug has been marked as a duplicate of 23177 ***