[main-custom] Support D8 bomb-workers

Merge over our internal changes to the main-custom branch.

Sources:
- https://crrev.com/i/7397481
- https://crrev.com/i/7431936
- https://crrev.com/i/7448617

Change-Id: I4dcb2042afecd3f84aed717f70356bb24a692ef5
Reviewed-on: https://chromium-review.googlesource.com/c/external/github.com/WebKit/JetStream/+/6651528
Reviewed-by: Daniel Lehmann <dlehmann@chromium.org>