Add extensions_unittests target to some Linux bots in chromium.fyi.

That way we get some coverage for this target on Linux too.

It might not even need a master restart, since I think this is using
recipes?

BUG=348066
TEST=these linux bots in master.chromium.fyi
R=sky@chromium.org

Review URL: https://codereview.chromium.org/311263006

git-svn-id: http://src.chromium.org/chrome/trunk/src/testing@275412 4ff67af0-8c30-449e-8e8b-ad334ec8d88c
Add athena_unittests to chromiumos

R=phajdan.jr@chromium.org, oshima@chromium.org
BUG=375537
TEST=Trybots

Review URL: https://codereview.chromium.org/314863004

git-svn-id: http://src.chromium.org/chrome/trunk/src/testing@275506 4ff67af0-8c30-449e-8e8b-ad334ec8d88c