Upstream service worker `client` tests to WPT

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

-self.onmessage = function(e) {
-  var port = e.data.port;
-  var message = [];
-
-  var promise = Promise.resolve()
-    .then(function() {
-        // 1st matchAll()
-        return self.clients.matchAll().then(function(clients) {
-            clients.forEach(function(client) {
-                message.push(client.id);
-              });
-          });
-      })
-    .then(function() {
-        // 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);
-      });
-  e.waitUntil(promise);
-};