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

LayoutTests/http/tests/serviceworker/resources/cache-storage-worker.js

-importScripts('worker-test-harness.js');
+importScripts('worker-testharness.js');
+importScripts('../../resources/testharness-helpers.js');
 
 promise_test(function(t) {
     var cache_name = 'cache-storage/foo';
     return self.caches.delete(cache_name)
       .then(function() {
           return self.caches.create(cache_name);
         })
       .then(function(cache) {
           assert_true(cache instanceof Cache,
                       'CacheStorage.create should return a Cache.');
@@ skipping 164 matching lines @@
 
 promise_test(function(t) {
     return self.caches.delete('cheezburger')
       .then(function(result) {
           assert_false(result,
                        'CacheStorage.delete should return false for a ' +
                        'nonexistent cache.');
         });
   }, 'CacheStorage.delete with nonexistent cache');