Chromium was apparently quite difficult to port to *BSD, the Google developers have attempted to make their official ports utilize features of the operating systems they initially attempted their port to, so the Linux/GTK port uses some Linux specific functionality.
Fortunately there has been work to port it to FreeBSD and OpenBSD, it may not have been accepted into FreeBSD just yet, but a unofficial port and some packages exist.
FreeBSD (Chromium 5, version 6 only for "subscribers"):
http://wiki.freebsd.org/Chromium
http://www.freebsd.org/cgi/query-pr.cgi?pr=146302
http://chromium.hybridsource.org/
http://chromium.hybridsource.org/port
OpenBSD (Chromium 5):
http://openports.se/www/chromium
http://sightly.net/peter/openbsd/chromium/
I haven't been able to test any of this myself, I don't run FreeBSD, and the package for OpenBSD/i386 needs a relatively newer system.