It is legal to stringify other kinds of values, like strings and numbers.
Since Local<Object> is convertible to Local<Value>, this is unlikely to
break callers.

Bug: v8:6810
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: Ie8e97c86308d62cdf0a2a17490a6e20de58fc76e
Reviewed-on: https://chromium-review.googlesource.com/657633Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47935}