Service Worker: Surface Client.id attribute.

LayoutTests/http/tests/serviceworker/resources/client-id-worker.js

+self.onmessage = function(e) {
+  var port = e.data.port;
+  var message = [];
+
+  // 1st matchAll()
+  self.clients.matchAll()
+    .then(function(clients) {
+        clients.forEach(function(client) {
+            message.push(client.id);
+          });
+      })
+    .then(function() {

[falken, 2015/06/25 04:09:56]

why is this a new function, it looks like the previous function doesn't return a
promise?

[jungkees, 2015/06/25 07:48:37]

The first forEach implicitly returns undefined, but it still guarantees the
second matchAll() is called after the client ids for the first matchAll() are
pushed in the result array. But I updated the code so it reads more clear in
that aspect.

+        // 2nd matchAll()
+        return self.clients.matchAll().then(function(clients) {
+            clients.forEach(function(client) {
+                message.push(client.id);
+              });
+          });
+      })
+    .then(function() {
+        // Send an array containing ids of clients from 1st and 2nd matchAll()
+        port.postMessage(message);
+      });
+};