If one input to JSStrictEqual/JSNotStrictEqual is Unique (except
InternalizedString) or the hole, then we can turn that into a
direct pointer comparison, as such values are only equal to exactly
the same unique value.

BUG=v8:5267
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2611363002
Cr-Commit-Position: refs/heads/master@{#42122}