Import w3c tests for the service workers

third_party/WebKit/LayoutTests/imported/wpt/service-workers/service-worker/resources/postmessage-msgport-to-client-worker.js

+self.onmessage = function(e) {
+  self.clients.matchAll().then(function(clients) {
+      clients.forEach(function(client) {
+          var messageChannel = new MessageChannel();
+          messageChannel.port1.onmessage =
+            onMessageViaMessagePort.bind(null, client);
+          client.postMessage({port: messageChannel.port2},
+                             [messageChannel.port2]);
+        });
+    });
+};
+
+function onMessageViaMessagePort(client, e) {
+  var message = e.data;
+  if ('value' in message) {
+    client.postMessage({ack: 'Acking value: ' + message.value});
+  } else if ('done' in message) {
+    client.postMessage({done: true});
+  }
+}