Implement redirect() API for Fetch Response

LayoutTests/http/tests/fetch/script-tests/headers-guard.js

 if (self.importScripts) {
   importScripts('../resources/fetch-test-helpers.js');
 }
 
 // Tests that invalid names/values throw TypeError.
 function testInvalidNamesAndValues(headers) {
   INVALID_HEADER_NAMES.forEach(function(name) {
       assert_throws({name: 'TypeError'},
                     function() { headers.append(name, 'a'); },
                     'Headers.append with an invalid name (' + name +
@@ skipping 350 matching lines @@
                         header + ' must be set (2)');
         });
   }, 'Headers guard = response: ResponseInit.headers');
 
 promise_test(function(t) {
   return fetch('../resources/doctype.html')
     .then(function(res) {
         [res.headers,
          res.clone().headers,
          Response.error().headers,
-         Response.error().clone().headers].forEach(function(headers) {
+         Response.error().clone().headers,
+         Response.redirect('https://www.example.com/test.html').headers,
+         Response.redirect('https://www.example.com/test.html').clone().headers
+        ].forEach(function(headers) {
             testInvalidNamesAndValues(headers);
 
             // Test that TypeError is thrown for all header names.
             FORBIDDEN_HEADER_NAMES
               .concat(FORBIDDEN_RESPONSE_HEADER_NAMES)
               .concat(SIMPLE_HEADER_NAMES)
               .concat([CONTENT_TYPE])
               .concat(NON_SIMPLE_HEADER_NAMES)
               .forEach(function(header) {
                   var value = headers.get(header);
@@ skipping 14 matching lines @@
                                 function() { headers.delete(header); },
                                 'Headers.delete(' + header + ') must throw');
                   assert_equals(headers.get(header), value,
                     'header ' + header + ' must be unchanged by delete()');
                 });
           });
       });
   }, 'Headers guard = immutable: set/append/delete');
 
 done();