Upstream foreign fetch tests.

third_party/WebKit/LayoutTests/external/wpt/service-workers/service-worker/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 /service-workers/service-worker/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 + new URL('resources/install-worker-helper.html', location).pathname)
+    .then(frame => new Promise((resolve, reject) => {
+        frame.contentWindow.postMessage({worker: worker,
+                                         options: {scope: scope}},
+                                        '*');
+        window.addEventListener('message', reply => {
+            if (reply.source != frame.contentWindow) return;
+            if (reply.data == 'success') resolve();
+            else reject(reply.data);
+          });
+      }));
+}
+
+// Performs a fetch from a different origin. By default this performs a fetch
+// from a window on that origin, but if |worker_type| is 'dedicated' or 'shared'
+// the fetch is made from a worker on that origin instead.
+// This uses a window rather than an iframe because an iframe might get blocked
+// by mixed content checks.
+function fetch_from_different_origin(origin, url, worker_type) {
+  const win = open(origin + new URL('resources/foreign-fetch-helper-iframe.html', location).pathname);
+  return new Promise(resolve => {
+        self.addEventListener('message', e => {
+            if (e.source != win) return;
+            resolve();
+          });
+      })
+    .then(() => new Promise((resolve) => {
+        const channel = new MessageChannel();
+        win.postMessage({url: url,
+                         worker: worker_type},
+                        '*', [channel.port1]);
+        channel.port2.onmessage = reply => {
+          win.close();
+          resolve(reply.data);
+        };
+      }));
+}