JSClassOf may lower to a call to a builtin, and needs to be
modeled in a way that the effect chain can be maintained.

Bug: v8:6929
Change-Id: Ida332e6d85e2eb8b33fcad810d195ef3e897ccb0
Reviewed-on: https://chromium-review.googlesource.com/727204Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48786}