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

LayoutTests/http/tests/resources/testharness-helpers.js

+/*
+ * testharness-helpers contains various useful extensions to testharness.js to
+ * allow them to be used across multiple tests before they have been
+ * upstreamed. This file is intended to be usable from both document and worker
+ * environments, so code should for example not rely on the DOM.
+ */
+
+// 'promise_test' is a new kind of testharness test that handles some
+// 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 reject.';
+    },
+    function(e) {
+      if (code !== undefined) {
+        assert_throws(code, function() { throw e; }, description);
+      }
+    });
+}