It's actually there to test now, if you don't mind using unstable versions. You need to switch the dev channel[1] and start the browser with --enable-extensions switch. There's a number of sample extensions already[2].

I've been running the dev channel builds for a while now and never had any major issues, only the occasional minor issue.

[1] http://dev.chromium.org/getting-involved/dev-channel [2] http://dev.chromium.org/developers/design-documents/extensio...