types of primitives, not just undefined, booleans, numbers, and strings.
(The missing cases were null and Symbol.) This is required by the
specification, and there are test262 tests which we were failing due to
this bug.

BUG=v8:5124

Review-Url: https://codereview.chromium.org/2096873002
Cr-Commit-Position: refs/heads/master@{#37234}