Upstream foreign fetch tests.

third_party/WebKit/LayoutTests/http/tests/serviceworker/resources/foreign-fetch-helpers.js

-// Common helper functions for foreign fetch tests.
-
-// Installs a service worker on a different origin. Both |worker| and |scope|
-// are resolved relative to the /serviceworker/resources/ directory on a
-// remote origin.
-function install_cross_origin_worker(
-    t, worker, scope, origin = get_host_info().HTTPS_REMOTE_ORIGIN) {
-  return with_iframe(origin +
-                     '/serviceworker/resources/install-worker-helper.html')
-    .then(frame => new Promise((resolve, reject) => {
-        var channel = new MessageChannel();
-        frame.contentWindow.postMessage({worker: worker,
-                                         options: {scope: scope},
-                                         port: channel.port1},
-                                        '*', [channel.port1]);
-        channel.port2.onmessage = reply => {
-            if (reply.data == 'success') resolve();
-            else reject(reply.data);
-          };
-      }));
-}