The ECMAScript ⊃ JSON proposal shipped in V8 v6.6 and Chrome 66.

Bug: v8:7418
Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: Id8979d0cec6d61ef4a7e9982142a3f3dcf7c326b
Reviewed-on: https://chromium-review.googlesource.com/1067857Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53271}