Add css-containment-debug as testcase #1
Description
A weak proposal.... but wanted to raise it.
I connected with @BioPhoton at the perfnow conference and he's a poweruser of the perf panel. Also.. check out https://github.com/push-based/css-contain-and-content-visibility-research#readme ! It's so good
Michael built https://css-containment-debug.stackblitz.io/ to isolate the different phases of rendering. And I suspect it might be useful for us as we update the PP.
That said, I will admit that I don't entirely grok the UI. @BioPhoton could you help explain it?