deps: cherry-pick c690f54d95802 from V8 upstream

Original commit message:

    [platform] Add TaskRunner to the platform API

    With the existing platform API it is not possible to post foreground
    tasks from background tasks. This is, however, required to implement
    asynchronous compilation for WebAssembly. With this CL we add the
    concept of a TaskRunner to the platform API. The TaskRunner contains
    all data needed to post a foreground task and can be used both from a
    foreground task and a background task. Eventually the TaskRunner should
    replace the existing API.

    In addition, this CL contains a default implementation of the
    TaskRunner. This implementation has tempory workaround for platforms
    which do not provide a TaskRunner implementation yet. This default
    implementation should be deleted again when all platforms provide a
    TaskRunner implementation.

    R=rmcilroy@chromium.org

    Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
    Change-Id: I6ea4a1c9da1eb9a19e8ce8f2163000dbc2598802
    Reviewed-on: https://chromium-review.googlesource.com/741588


    Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#49041}

Refs: https://github.com/v8/v8/commit/c690f54d9580243c53f7d892fcff1ce6bae4bfc0

PR-URL: https://github.com/nodejs/node/pull/17134
Fixes: https://github.com/nodejs/node-v8/issues/24


Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>