PreParser and Parser didn't agree whether a generator in a sloppy block is a
sloppy block function or not, and thus the data generated by PreParser was
inconsistent with what the Parser wanted to restore.

BUG=v8:5516, chromium:760116

Change-Id: I0fd3c267691b8afd63a1336774769caf551c143e
Reviewed-on: https://chromium-review.googlesource.com/642886Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47727}