Merge base unit tests into src to be in line with Chrome.

We still need the test/base-unittests folder until the test driver is
updated to handle unittests without the boilerplate.

TEST=base-unittests
R=svenpanne@chromium.org
BUG=v8:3489
LOG=n

Review URL: https://codereview.chromium.org/520503004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23516 ce2b1a6d-e550-0410-aec6-3dcde31c8c00