ServiceWorker: "minimal" end-to-end sample as a W3C test

LayoutTests/http/tests/serviceworker/resources/support.js

+// Service Worker helpers for testharness.js-based tests.
+
+// Use with unexpected event handlers or Promise rejection. Will
+// fail the test with a name/message is present on the error.
+// E.g.:
+//    onbadevent = fail(t, 'Should only see good events');
+//    Promise.then(...).catch(fail(t, 'Rejection is never fun'));
+function fail(test, desc) {
+    desc = desc || 'Failure';
+    return test.step_func(function(reason) {
+        if (reason && 'name' in reason && 'message' in reason) {
+            assert_unreached(desc + ': ' + reason.name + ' - ' + reason.message);
+        } else if (reason && 'name' in reason) {
+            assert_unreached(desc + ': ' + reason.name);
+        } else {
+            assert_unreached(desc);
+        }
+    });
+}
+
+// Sends a message of {port, from} to the specified worker, and returns the
+// port at the local end of the channel.
+function sendMessagePort(worker, from) {
+    var messageChannel = new MessageChannel();
+    worker.postMessage({from:from, port:messageChannel.port2}, [messageChannel.port2]);
+    return messageChannel.port1;
+}