This function currently causes a forced layout, which makes the display of the DOM choppy. It's invoked soon after firstPaint, which is a time where a lot of stuff runs. It would be better for visual performance to either do it later or to just not do it at all. Since the line causing it is about doing feature detection, maybe there are alternative ways of testing for those browser features that doesn't cause a forced layout.
This article highlights a technique for detecting CSS animation support which seems like a much lighter technique than the one currently used by supportsAnimation: https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Using_CSS_animations/Detecting_CSS_animation_support
I also suspect that the technique currently used might just not actually need getComputedStyle and could just read the style back, like it's done in that Mozilla article.