Worker: Run WPT for service workers with off-the-main-thread dedicated/shared worker script fetch

Bug: 835717, 906991, 924041
Change-Id: I5402968652cf1818fa865fe63d213b31453b84c4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1510706
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638937}
4 files changed