Issue #2641 - Update Fetch to adhere to the updated spec (pass refpolicy)

Resolves #2641

dom/xhr/XMLHttpRequestMainThread.cpp

@@ -2434,9 +2434,10 @@ XMLHttpRequestMainThread::InitiateFetch(nsIInputStream* aUploadStream,
     if (!IsSystemXHR()) {
       nsCOMPtr<nsPIDOMWindowInner> owner = GetOwner();
       nsCOMPtr<nsIDocument> doc = owner ? owner->GetExtantDoc() : nullptr;
+      mozilla::net::ReferrerPolicy referrerPolicy = doc ?
+        doc->GetReferrerPolicy() : mozilla::net::RP_Default;
       nsContentUtils::SetFetchReferrerURIWithPolicy(mPrincipal, doc,
-                                                    httpChannel,
-                                                    mozilla::net::RP_Default);
+                                                    httpChannel, referrerPolicy);
     }
 
     // Some extensions override the http protocol handler and provide their own