[V8] Added Script::is_opaque flag for embedders

[V8] Added Script::is_opaque flag for embedders

When the page is controlled by a ServiceWorker, the ServiceWorker can return an opaque (non-CORS cross origin) resource response.
We need to treat the messages from such script resource as opaque.

Committed: https://crrev.com/7a599c5e1242d3c5ab7515ee149623da90ae69ec
Cr-Commit-Position: refs/heads/master@{#28445}

Review URL: https://codereview.chromium.org/1140673002

Cr-Commit-Position: refs/heads/master@{#28459}