Add tests for TypeImpl::Of(), TypeImpl::NowOf() and
TypeImpl::NowContains(). Improves the implementation of
TypeImpl::NowIs() to match that of TypeImpl::NowContains().
Mark test-types with NO_VARIANTS to speedup testing, since
the variants do not affect the type system at all.
Also improve test coverage for types.
TEST=cctest/test-types
R=rossberg@chromium.org
Review URL: https://codereview.chromium.org/230673002
git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20639 ce2b1a6d-e550-0410-aec6-3dcde31c8c00