deps: check in gtest, add util unit test

Check in a gypified gtest and add a simple unit test to show that the
basic infrastructure is in place.

PR-URL: https://github.com/iojs/io.js/pull/1199
Refs: https://github.com/iojs/io.js/issues/1193


Reviewed-By: Fedor Indutny <fedor@indutny.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>