Upstream service worker message event tests to WPT

third_party/WebKit/LayoutTests/http/tests/serviceworker/ServiceWorkerGlobalScope/resources/extendable-message-event-worker.js

-self.addEventListener('message', function(event) {
-    var results = [
-        'Client message: ' + event,
-        '  event.origin: ' + event.origin,
-        '  event.lastEventId: ' + event.lastEventId,
-        '  event.source: ' + event.source,
-        '  event.source.url: ' + event.source.url,
-        '  event.source.frameType: ' + event.source.frameType,
-        '  event.source.visibilityState: ' + event.source.visibilityState,
-        '  event.source.focused: ' + event.source.focused,
-        '  event.ports: ' + event.ports,
-    ];
-    event.source.postMessage(results);
-  });