Move promise_test and assert_promise_rejects out of worker-test-harness.

LayoutTests/http/tests/serviceworker/resources/headers-worker.js

-importScripts('worker-test-harness.js');
+importScripts('worker-testharness.js');
 
 test(function() {
     function size(headers) {
       var count = 0;
       for (var header of headers) {
         ++count;
       }
       return count;
     }
 
@@ skipping 184 matching lines @@
     assert_throws({name:'TypeError'},
                   function() { var headers = new Headers([['a']]); },
                   'new Headers with a sequence with less than two strings should throw');
     assert_throws({name:'TypeError'},
                   function() { var headers = new Headers([['a', 'b'], []]); },
                   'new Headers with a sequence with less than two strings should throw');
     assert_throws({name:'TypeError'},
                   function() { var headers = new Headers([['a', 'b'], ['x', 'y', 'z']]); },
                   'new Headers with a sequence with more than two strings should throw');
 }, 'Headers in ServiceWorkerGlobalScope');