The memory gains were significant, so despite the bluebird-doxbee
regression, we think it's better to have this patch than not.
See the attached Chromium bug for more discussion.

This is a reland of 20e346bd.

Original change's description:
> [parser] Remove pretenuring of closures assigned to properties
>
> This pretenuring was added in https://codereview.chromium.org/5220007,
> back when it was necessary in order to allow use of the closure
> as a "constant function" property. This should no longer be the case,
> and the pretenuring causes some unfortunate downstream effects.
>
> This patch removes the parser's setting of this bit. If it doesn't
> cause regressions on the perf bots, followup CLs will remove the
> rest of the support for this feature.
>
> Bug: v8:7442
> Change-Id: I27c43dd4293ce5de921be6c78571e712778d138a
> Reviewed-on: https://chromium-review.googlesource.com/914610
> Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
> Commit-Queue: Adam Klein <adamk@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#51254}

Bug: v8:7442, chromium:814182
Change-Id: I228c59dccef3844803f115749e72ae6c5f286eda
Reviewed-on: https://chromium-review.googlesource.com/938241Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51668}