It is possible, though unlikely, that V8 will deserialize code cache
data, decide to merge that new data with an existing script from the
Isolate compilation cache, and subsequently do nothing in the background
portion of the merge (make no heap changes, and request no follow-up
changes on the main thread). In this case, the most optimal outcome is
to reuse the script from the Isolate compilation cache, not to use the
newly deserialized script.

CodeSerializer::FinishOffThreadDeserialize uses
BackgroundMergeTask::HasPendingForegroundWork to determine whether it
should complete the merge and use the Script from the compilation cache
or complete the deserialization and use the newly deserialized Script.
This change updates HasPendingForegroundWork so that it will return true
even if the merge was a no-op.

Bug: v8:12808
Change-Id: I08fcb814e797218e5be2b4ce4f45bd4e0637ec80
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3916270
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83439}