Refactoring: Make gtest testsuite the default.

BUG=v8:3489
R=bmeurer@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/526133003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23583 ce2b1a6d-e550-0410-aec6-3dcde31c8c00