Revert of Split PendingScript into PendingScript and ClassicPendingScript (patchset #37 id:720001 of https://codereview.chromium.org/2653923008/ )

Reason for revert:
Suspected to cause CHECK() failure (crbug.com/711703)
inside PendingScript's prefinalizer.

BUG=711703

Original issue's description:
> Split PendingScript into PendingScript and ClassicPendingScript
>
> This is preparation for introducing ModulePendingScript.
>
> BUG=594639, 686281
>
> Review-Url: https://codereview.chromium.org/2653923008
> Cr-Commit-Position: refs/heads/master@{#464494}
> Committed: https://chromium.googlesource.com/chromium/src/+/d512803299c01324b92ffd8c962da97e3bc8ccff

TBR=kouhei@chromium.org,sigbjornf@opera.com,japhet@chromium.org,haraken@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=594639, 686281

Review-Url: https://codereview.chromium.org/2820753002
Cr-Commit-Position: refs/heads/master@{#464768}
10 files changed