This will allow V8 extra consumers to track promise state without
using a side-table. This is used by streams as of
https://github.com/whatwg/streams/commit/173f9f67be56f6690f82ec26fe86c8e67256616b.

BUG=chromium:658144

Review-Url: https://codereview.chromium.org/2784213002
Cr-Commit-Position: refs/heads/master@{#44287}