Add Mavericks to test config.

BUG=338160
TEST=gpu_unittests on 10.9 bots
R=kbr@chromium.org

Review URL: https://codereview.chromium.org/141753015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248647 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248647