Limit foreign fetch to only intercept requests made from secure contexts.

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) {
-  return with_iframe(get_host_info().HTTPS_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);
           };
       }));
 }