On: Chrome DevTools could do that?

[statictype]

Crap, there's a lot of useful stuff in there.

The paint rectangles thing is amazing. I didn't know browsers even expose this data.

The Audit API looks really useful too. I'm now thinking of standardizing on Chrome as the development browser for our team (most devs prefer it anyway) so we can share custom development tool add-ons.

[mbrubeck → statictype]

Firefox also has a way to expose invalidation rectangles:

http://www.junglecode.net/?p=110