chromium-20.0.1105.0 didn't compile with =dev-lang/v8-3.9.13, complaining about a missing a function in v8. Updating to the latest 3.10.x version of v8 helped. Guess all 20 versions need the newer v8.
Thanks for letting us know. I have updated the latest chromium-20.x ebuild; the older one will be removed from the tree soon anyway. + 22 Apr 2012; Mike Gilbert <floppym@gentoo.org> chromium-20.0.1105.0.ebuild: + Update v8 dependency per bug 413127. +