I know about that tool, but for JS you can dig and find the hot spots with painting operations you could not find what css triggered them. I could use them to identify JS code that did too much DOM changes and optimize them though.
If you make a performance recording of the page, you can then select the main thread, open event log, and filter by "Layout". You won't get a summarized overview, but you can see the layout root for each entry, which will show you what caused the layout update. For complex pages with numerous parallel animations, you might need to filter this data more, but for example in the article we're discussing right now, manual checking quickly reveals where the layout updates are coming form.
