deps: cherry-pick 68e89fb from v8's upstream

Original commit message:

    This commit adds some postmortem data that is otherwise unavailable.

    I have discovered need in those values when writing:

    https://github.com/indutny/llnode

    BUG=

    Review URL: https://codereview.chromium.org/1436473002

    Cr-Commit-Position: refs/heads/master@{#31947}

This postmortem information is useful for both object inspection, and
function's context variables inspection.

Ref: https://github.com/nodejs/node/pull/3779
PR-URL: https://github.com/nodejs/node/pull/4106


Reviewed-By: bnoordhuis - Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: targos - Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: rvagg - Rod Vagg <rod@vagg.org>