This allows us to preserve the script URL when importing a module in a
worker.

R=ahaas@chromium.org,clemensb@chromium.org
CC=kimanh@chromium.org

Bug: chromium:1064548
Change-Id: Id5e48c840e2dba8eadb5c854fcb389787ce11215
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2167866
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67543}