The goal of this specification is to allow webpages to control the behaviour of the Referer header (sic) when network requests are initiated.

The basic pieces here are the following:

create an enum representing a referrer policy in net_traits/lib.rs
introduce a place where referrer policies are stored for global environments (ie. Document and WorkerGlobalScope, in document.rs and workerglobalscope.rs respectively)
propagate this policy to the actual HTTP network request code in http_loader.rs and modify the Referer header accordingly (via document_loader.rs, fetch the policy from the global environment)
introduce per-element attributes for controlling the associated requests, ensure those get propagated accordingly (eg. htmlscriptelement.rs, htmliframeelement.rs, etc.)
integrate with the Fetch implementation (components/net/fetch/methods.rs) and write unit tests (tests/unit/net/fetch.rs)
support setting the initial global policy via the Referrer-Policy HTTP header in the initial network response for a worker/document (in http_loader.rs, add a new field to the Metadata type and extract that when creating the new Document in script_thread.rs)

Implement referrer policy #10311

Description