Add cast_unittests to chromium_builder_tests.

BUG=306567
R=maruel@chromium.org

Review URL: https://codereview.chromium.org/109383006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241555 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241555