Revert of Remove ineffective PendingScript prefinalizer (2nd attempt.) (patchset #1 id:1 of https://codereview.chromium.org/2060853002/ )

Reason for revert:
Canary crashes reported,

 https://bugs.chromium.org/p/chromium/issues/detail?id=615977#c12

Original issue's description:
> Remove ineffective PendingScript prefinalizer (2nd attempt.)
>
> With the missing case from r397106 aboard, retire the prefinalizer
> for PendingScript. Script loader and runner objects are expected
> to explicitly dispose of these upon success or failure.
>
> R=
> BUG=
>
> Committed: https://crrev.com/fbf7f01ae80f666a5b37acf0ef38fd174443787f
> Cr-Commit-Position: refs/heads/master@{#399504}

TBR=haraken@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review-Url: https://codereview.chromium.org/2069573002
Cr-Commit-Position: refs/heads/master@{#399691}
2 files changed