Revert of JSObject::GetEnumProperty cleanup (patchset #2 id:20001 of https://codereview.chromium.org/1363293002/ )

Reason for revert:
Reverting, because of broken GC stress bots.

@cbruni: Sorry for the revert. I'm not entirely sure it's actually your CL; but policy is to revert speculatively if we can't determine an exact cause.

Original issue's description:
> JSObject::GetEnumProperty cleanup
>
> BUG=
>
> Committed: https://crrev.com/a00d47c802f93cf9835eafce4c9da2dd10b44f6a
> Cr-Commit-Position: refs/heads/master@{#30946}

TBR=jkummerow@chromium.org,cbruni@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1371673004

Cr-Commit-Position: refs/heads/master@{#30950}