Reland of Ship ES2015 sloppy-mode function hoisting, let, class (patchset #1 id:1 of https://codereview.chromium.org/1565263002/ )

Reason for revert:
Crash fixed by https://codereview.chromium.org/1564923007

Original issue's description:
> Revert of Ship ES2015 sloppy-mode function hoisting, let, class (patchset #7 id:120001 of https://codereview.chromium.org/1551443002/ )
>
> Reason for revert:
> Causes frequent crashes in Canary: chromium:537816
>
> Original issue's description:
> > Ship ES2015 sloppy-mode function hoisting, let, class
> >
> > This patch doesn't ship all features of ES2015 variable/scoping
> > changes, notably omitting the removal of legacy const. I think
> > function hoisting, let and class in sloppy mode can stand to
> > themselves as a package, and the legacy const change is much
> > riskier and more likely to be reverted, so my intention is to
> > pursue those as a separate, follow-on patch.
> >
> > R=adamk@chromium.org
> > BUG=v8:4285,v8:3305
> > LOG=Y
> > CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel
> >
> > Committed: https://crrev.com/fcff8588a5a01587643d6c2507c7b882c78a2957
> > Cr-Commit-Position: refs/heads/master@{#33133}
>
> TBR=adamk@chromium.org
> # Not skipping CQ checks because original CL landed more than 1 days ago.
> BUG=v8:4285,v8:3305,chromium:537816
> LOG=Y
>
> Committed: https://crrev.com/adac5956c6216056a211cfaa460a00ac1500d8f8
> Cr-Commit-Position: refs/heads/master@{#33162}

TBR=adamk@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4285,v8:3305,chromium:537816

Review URL: https://codereview.chromium.org/1571793002

Cr-Commit-Position: refs/heads/master@{#33189}