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
Review URL: https://codereview.chromium.org/1565263002
Cr-Commit-Position: refs/heads/master@{#33162}
adac5956c6