Prerender: Add WPT for worker creation in cross-origin iframes

Bug: 1424250
Change-Id: Ib956dbdea5ccba8684f3d3e03571e56e8c333a2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4339339


Reviewed-by: Lingqi Chi <lingqi@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1117915}