Reland of [heap] Simplify marking of JSFunction and SFI (patchset #1 id:1 of https://codereview.chromium.org/2389963007/ )

Reason for revert:
Wrong culprit as this was already broken before.

Original issue's description:
> Revert of [heap] Simplify marking of JSFunction and SFI (patchset #3 id:40001 of https://codereview.chromium.org/2389183002/ )
>
> Reason for revert:
> Broke GCStress.
>
> Original issue's description:
> > [heap] Simplify marking of JSFunction and SFI
> >
> > BUG=chromium:651828
> >
> > Committed: https://crrev.com/4d45ed4597d537cf9624cb6683dc4bd646d11242
> > Cr-Commit-Position: refs/heads/master@{#39975}
>
> TBR=hpayer@chromium.org,mlippautz@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=chromium:651828
>
> Committed: https://crrev.com/5295d7a463cbcc78a4b694a7fb84af8e8e400303
> Cr-Commit-Position: refs/heads/master@{#39983}

TBR=hpayer@chromium.org,epertoso@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:651828

Review-Url: https://codereview.chromium.org/2390373004
Cr-Commit-Position: refs/heads/master@{#39990}