Import //fetch from Web Platform Tests.

third_party/WebKit/LayoutTests/external/wpt/fetch/api/cors/cors-preflight-referrer.js

+if (this.document === undefined) {
+  importScripts("/resources/testharness.js");
+  importScripts("/common/utils.js");
+  importScripts("/common/get-host-info.sub.js");
+  importScripts("../resources/utils.js");
+}
+
+function corsPreflightReferrer(desc, corsUrl, referrerPolicy, referrer, expectedReferrer) {
+  var uuid_token = token();
+  var url = corsUrl;
+  var urlParameters = "?token=" + uuid_token + "&max_age=0";
+  var requestInit = {"mode": "cors", "referrerPolicy": referrerPolicy};
+
+  if (referrer)
+      requestInit.referrer = referrer;
+
+  /* Force preflight */
+  requestInit["headers"] = {"x-force-preflight": ""};
+  urlParameters += "&allow_headers=x-force-preflight";
+
+  promise_test(function(test) {
+    return fetch(RESOURCES_DIR + "clean-stash.py?token=" + uuid_token).then(function(resp) {
+      assert_equals(resp.status, 200, "Clean stash response's status is 200");
+      return fetch(url + urlParameters, requestInit).then(function(resp) {
+        assert_equals(resp.status, 200, "Response's status is 200");
+        assert_equals(resp.headers.get("x-did-preflight"), "1", "Preflight request has been made");
+        assert_equals(resp.headers.get("x-preflight-referrer"), expectedReferrer, "Preflight's referrer is correct");
+        assert_equals(resp.headers.get("x-referrer"), expectedReferrer, "Request's referrer is correct");
+        assert_equals(resp.headers.get("x-control-request-headers"), "", "Access-Control-Allow-Headers value");
+      });
+    });
+  }, desc + " and referrer: " + (referrer ? "'" + referrer + "'" : "default"));
+}
+
+var corsUrl = get_host_info().HTTP_REMOTE_ORIGIN  + dirname(location.pathname) + RESOURCES_DIR + "preflight.py";
+var origin = get_host_info().HTTP_ORIGIN + "/";
+
+corsPreflightReferrer("Referrer policy: no-referrer", corsUrl, "no-referrer", undefined, "");
+corsPreflightReferrer("Referrer policy: no-referrer", corsUrl, "no-referrer", "myreferrer", "");
+
+corsPreflightReferrer("Referrer policy: \"\"", corsUrl, "", undefined, location.toString())
+corsPreflightReferrer("Referrer policy: \"\"", corsUrl, "", "myreferrer", new URL("myreferrer", location).toString());
+
+corsPreflightReferrer("Referrer policy: origin", corsUrl, "origin", undefined, origin);
+corsPreflightReferrer("Referrer policy: origin", corsUrl, "origin", "myreferrer", origin);
+
+corsPreflightReferrer("Referrer policy: origin-when-cross-origin", corsUrl, "origin-when-cross-origin", undefined, origin);
+corsPreflightReferrer("Referrer policy: origin-when-cross-origin", corsUrl, "origin-when-cross-origin", "myreferrer", origin);
+
+corsPreflightReferrer("Referrer policy: unsafe-url", corsUrl, "unsafe-url", undefined, location.toString());
+corsPreflightReferrer("Referrer policy: unsafe-url", corsUrl, "unsafe-url", "myreferrer", new URL("myreferrer", location).toString());
+
+done();