Add browser_test to the mac builders, doesn't pass yet, but this way it's ready to be run when it works.

BUG=none
TEST=none
Review URL: http://codereview.chromium.org/256052

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@27993 0039d316-1c4b-4281-b951-d872f2087c98