The chromium ebuild might be missing a dependency. Several people (myself included) have emerged chromium, only to find that chromium-setup and chromium simply exit with a segfault on running. I find that even downloading chromium from their website and attempting to build produces the same error.
What USE variables are you using?
Use variables are: pda slang readline gpm berkdb gdbm tcpd pam libwww ssl alsa nls mitshm perl python esd gif sdl vorbis ogg gtk X qt motif opengl mozilla lame mmx 3dnow cups
I should also mention that I'm using the latest XFree86 ebuild and the latest NVIDIA driver. TuxRacer and Quake3 both work fine for me. I also attempted to manually download and install chromium, but had the exact same result. This is disturbing, since I meet the requirements on the chromium web page (sdl and nvidia)
try to do an "strace" on chromium; hopefully that will show what is happening.
Huh. An emerge update --world seems to have fixed it. Nevermind.
kewlies!