[ServiceWorker] CacheStorage tests.

LayoutTests/http/tests/serviceworker/resources/worker-test-harness.js

 /*
  * worker-test-harness should be considered a temporary polyfill around
  * testharness.js for supporting Service Worker based tests. It should not be
  * necessary once the test harness is able to drive worker based tests natively.
  * See https://github.com/w3c/testharness.js/pull/82 for status of effort to
  * update upstream testharness.js. Once the upstreaming is complete, tests that
  * reference worker-test-harness should be updated to directly import
  * testharness.js.
  */
 
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 // boilerplate for testing with promises.
 function promise_test(func, name, properties) {
   properties = properties || {};
   var test = async_test(name, properties);
   Promise.resolve(test.step(func, test, test))
     .then(function() { test.done(); })
     .catch(test.step_func(function(value) {
         throw value;
       }));
 }
+
+// Returns a promise that fulfills after the provided |promise| is fulfilled.
+// The |test| succeeds only if |promise| rejects with an exception matching
+// |code|. Accepted values for |code| follow those accepted for assert_throws().
+// The optional |description| describes the test being performed.
+// E.g.:
+//   assert_promise_rejects(
+//       new Promise(...), // something that should throw an exception.
+//       'NotFoundError',
+//       'Should throw NotFoundError.');
+//
+//   assert_promise_rejects(
+//       new Promise(...),
+//       new TypeError(),
+//       'Should throw TypeError');
+function assert_promise_rejects(promise, code, description) {
+  return promise.then(
+    function() {
+      throw 'assert_promise_rejects: ' + description + ' Promise did not throw.';
+    },
+    function(e) {
+      if (code !== undefined) {
+        assert_throws(code, function() { throw e; }, description);
+      }
+    });
+}