Import //fetch from Web Platform Tests.

third_party/WebKit/LayoutTests/external/wpt/fetch/api/basic/request-referrer.js

+if (this.document === undefined) {
+  importScripts("/resources/testharness.js");
+  importScripts("../resources/utils.js");
+}
+
+function testReferrer(referrer, expected, desc) {
+  promise_test(function(test) {
+    var url = RESOURCES_DIR + "inspect-headers.py?headers=referer"
+    var req = new Request(url, { referrer: referrer });
+    return fetch(req).then(function(resp) {
+      var actual = resp.headers.get("x-request-referer");
+      if (expected) {
+        assert_equals(actual, expected, "request's referer should be: " + expected);
+        return;
+      }
+      if (actual) {
+        assert_equals(actual, "", "request's referer should be empty");
+      }
+    });
+  }, desc);
+}
+
+testReferrer("about:client", self.location.href, 'about:client referrer');
+
+var fooURL = new URL("./foo", self.location).href;
+testReferrer(fooURL, fooURL, 'url referrer');
+
+done();