See
https://webassembly.github.io/mutable-global/js-api/index.html#globals
for the current spec.

Bug: v8:7625

Change-Id: I70f567a9a0c6fc44c04c245ff496386941a699a9
Reviewed-on: https://chromium-review.googlesource.com/999168
Commit-Queue: Ben Smith <binji@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52494}