Implement Referrer-Policy header for workers

third_party/WebKit/LayoutTests/http/tests/security/referrerPolicyHeader/resources/worker.php

+<?
+header('Content-Type: application/javascript');
+header('Referrer-Policy: origin');
+?>
+importScripts('save-referrer.php');
+
+// When loaded as a shared worker, send the referrer on connect.
+onconnect = function (e) {
+  var port = e.ports[0];
+  port.postMessage(referrer);
+}
+
+// When loaded as a dedicated worker, send the referrer to the document immediately.
+postMessage(referrer);