Upstream service worker message event tests to WPT

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

-self.addEventListener('message', function(event) {
-    switch (event.data.type) {
-      case 'start':
-        // Send a ping message to another service worker.
-        self.registration.waiting.postMessage(
-            {type: 'ping', client_id: event.source.id});
-        break;
-      case 'pong':
-        var results = [
-            'Pong message: ' + event,
-            '  event.origin: ' + event.origin,
-            '  event.lastEventId: ' + event.lastEventId,
-            '  event.source: ' + event.source,
-            '  event.source.scriptURL: ' + event.source.scriptURL,
-            '  event.source.state: ' + event.source.state,
-            '  event.ports: ' + event.ports,
-        ];
-        var client_id = event.data.client_id;
-        event.waitUntil(clients.get(client_id)
-            .then(function(client) {
-                client.postMessage({type: 'record', results: results});
-                client.postMessage({type: 'finish'});
-              }));
-        break;
-    }
-  });