deps: cherry-pick 1aead19 from upstream V8

Original commit message:

    Add postmortem metadata for thin strings.

    See: https://github.com/nodejs/llnode/issues/117
    Change-Id: Icc2830c8e9096610df33ffdc2f89e74cb1b35662
    Reviewed-on: https://chromium-review.googlesource.com/618986


Reviewed-by: Michael Achenbach <machenbach@chromium.org>
    Commit-Queue: Ben Noordhuis <info@bnoordhuis.nl>
    Cr-Commit-Position: refs/heads/master@{#47778}

PR-URL: https://github.com/nodejs/node/pull/15184
Ref: https://github.com/nodejs/llnode/issues/117
Ref: https://github.com/nodejs/llnode/pull/121


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>