Fetch API: Fix behavior when Request constructor is passed an undefined referrer

third_party/WebKit/LayoutTests/http/tests/fetch/script-tests/request.js

 if (self.importScripts) {
   importScripts('../resources/fetch-test-helpers.js');
 }
 
 var URL = 'https://www.example.com/test.html';
 
 test(function() {
     var headers = new Headers;
     headers.set('User-Agent', 'Mozilla/5.0');
     headers.set('Accept', 'text/html');
@@ skipping 385 matching lines @@
     assert_true(req.bodyUsed,
                 'Request should be flagged as used if it has been consumed.');
   }, 'Request construction failure should not set "bodyUsed"');
 
 test(function() {
     assert_equals(new Request(URL).referrer, 'about:client');
     assert_equals(new Request(URL).referrerPolicy, '');
   }, 'Request without RequestInit.');
 
 test(function() {
+  assert_equals(new Request(URL, {referrer: undefined}).referrer,
+               'about:client');
+  assert_equals(new Request(URL).referrerPolicy, '');
+}, 'Request with referrer equals to undefined.');
+
+test(function() {
+  var expected = location.href.slice(0, location.href.lastIndexOf('/')) +
+    '/null';
+  assert_equals(new Request(URL, {referrer: null}).referrer, expected);
+  assert_equals(new Request(URL).referrerPolicy, '');
+}, 'Request with referrer equals to null.');
+
+test(function() {
     var req = new Request(URL, {referrer: 'about:client'});
 
     assert_equals(req.referrer, 'about:client',
                   'constructed with referrer=about:client');
     assert_equals(new Request(req.clone()).referrer, 'about:client',
                  'cloned from a request with referrer=about:client');
     assert_equals(new Request(req.clone(), {foo: null}).referrer,
                   'about:client',
                   'constructed from a request with referrer=about:client');
     assert_equals(new Request(req.clone(), {method: 'GET'}).referrer,
@@ skipping 397 matching lines @@
                            credentials: 'include',
                            body: 'this is a body'});
 
     return req.text()
         .then(t => {
            assert_equals(t, 'this is a body');
         });
   }, 'Credentials and body can both be set.');
 
 done();