--- a/testing/web-platform/tests/resources/testharness.js
+++ b/testing/web-platform/tests/resources/testharness.js
@@ -393,30 +393,17 @@ policies and contribution forms [3].
     function ServiceWorkerTestEnvironment() {
         WorkerTestEnvironment.call(this);
         this.all_loaded = false;
         this.on_loaded_callback = null;
         var this_obj = this;
         self.addEventListener("message",
                 function(event) {
                     if (event.data && event.data.type && event.data.type === "connect") {
-                        if (event.ports && event.ports[0]) {
-                            // If a MessageChannel was passed, then use it to
-                            // send results back to the main window.  This
-                            // allows the tests to work even if the browser
-                            // does not fully support MessageEvent.source in
-                            // ServiceWorkers yet.
-                            this_obj._add_message_port(event.ports[0]);
-                            event.ports[0].start();
-                        } else {
-                            // If there is no MessageChannel, then attempt to
-                            // use the MessageEvent.source to send results
-                            // back to the main window.
-                            this_obj._add_message_port(event.source);
-                        }
+                        this_obj._add_message_port(event.source);
                     }
                 }, false);
 
         // The oninstall event is received after the service worker script and
         // all imported scripts have been fetched and executed. It's the
         // equivalent of an onload event for a document. All tests should have
         // been added by the time this event is received, thus it's not
         // necessary to wait until the onactivate event. However, tests for

--- a/testing/web-platform/tests/service-workers/service-worker/client-navigate.https.html
+++ b/testing/web-platform/tests/service-workers/service-worker/client-navigate.https.html
@@ -33,21 +33,23 @@
   }
 
   promise_test(function(t) {
     var worker = "resources/client-navigate-worker.js";
     var scope = "resources/client-navigate-frame.html";
     var controller, frame, clientId;
 
     return service_worker_unregister_and_register(t, worker, scope)
-      .then(reg => wait_for_state(t, reg.installing, "activated"))
+      .then(reg => {
+        controller = reg.installing;
+        return wait_for_state(t, reg.installing, "activated");
+      })
       .then(___ => with_iframe(scope))
       .then(f => {
         frame = f;
-        controller = frame.contentWindow.navigator.serviceWorker.controller;
         fetch_tests_from_worker(controller);
         return wait_for_message()
       })
       .then(({id}) => clientId = id)
       .then(___ => run_test(controller, clientId, "test_client_navigate_success"))
       .then(({result, url}) => {
         assert_equals(result, "test_client_navigate_success");
         assert_equals(
@@ -64,21 +66,23 @@
   }, "Frame location should update on successful navigation");
 
   promise_test(function(t) {
     var worker = "resources/client-navigate-worker.js";
     var scope = "resources/client-navigate-frame.html";
     var controller, frame, clientId;
 
     return service_worker_unregister_and_register(t, worker, scope)
-      .then(reg => wait_for_state(t, reg.installing, "activated"))
+      .then(reg => {
+        controller = reg.installing;
+        return wait_for_state(t, reg.installing, "activated");
+      })
       .then(___ => with_iframe(scope))
       .then(f => {
         frame = f;
-        controller = frame.contentWindow.navigator.serviceWorker.controller;
         fetch_tests_from_worker(controller);
         return wait_for_message()
       })
       .then(({id}) => clientId = id)
       .then(___ => run_test(controller, clientId, "test_client_navigate_redirect"))
       .then(({result, url}) => {
         assert_equals(result, "test_client_navigate_redirect");
         assert_equals(url, "");
@@ -90,21 +94,23 @@
   }, "Frame location should not be accessible after redirect");
 
   promise_test(function(t) {
     var worker = "resources/client-navigate-worker.js";
     var scope = "resources/client-navigate-frame.html";
     var controller, frame, clientId;
 
     return service_worker_unregister_and_register(t, worker, scope)
-      .then(reg => wait_for_state(t, reg.installing, "activated"))
+      .then(reg => {
+        controller = reg.installing;
+        return wait_for_state(t, reg.installing, "activated");
+      })
       .then(___ => with_iframe(scope))
       .then(f => {
         frame = f;
-        controller = frame.contentWindow.navigator.serviceWorker.controller;
         fetch_tests_from_worker(controller);
         return wait_for_message()
       })
       .then(({id}) => clientId = id)
       .then(___ => run_test(controller, clientId, "test_client_navigate_cross_origin"))
       .then(({result, url}) => {
         assert_equals(result, "test_client_navigate_cross_origin");
         assert_equals(url, "");
@@ -116,21 +122,23 @@
   }, "Frame location should not be accessible after cross-origin navigation");
 
   promise_test(function(t) {
     var worker = "resources/client-navigate-worker.js";
     var scope = "resources/client-navigate-frame.html";
     var controller, frame, clientId;
 
     return service_worker_unregister_and_register(t, worker, scope)
-      .then(reg => wait_for_state(t, reg.installing, "activated"))
+      .then(reg => {
+        controller = reg.installing;
+        return wait_for_state(t, reg.installing, "activated");
+      })
       .then(___ => with_iframe(scope))
       .then(f => {
         frame = f;
-        controller = frame.contentWindow.navigator.serviceWorker.controller;
         fetch_tests_from_worker(controller);
         return wait_for_message()
       })
       .then(({id}) => clientId = id)
       .then(___ => run_test(controller, clientId, "test_client_navigate_about_blank"))
       .then(({result, url}) => {
         assert_equals(result, "test_client_navigate_about_blank");
         assert_equals(
@@ -146,22 +154,22 @@
 
   promise_test(function(t) {
     var worker = "resources/client-navigate-worker.js";
     var scope = "resources/client-navigate-frame.html";
     var controller, frame, clientId;
 
     return service_worker_unregister_and_register(t, worker, scope)
       .then(reg => {
+        controller = reg.installing;
         return wait_for_state(t, reg.installing, "activated");
       })
       .then(___ => with_iframe(scope))
       .then(f => {
         frame = f;
-        controller = frame.contentWindow.navigator.serviceWorker.controller;
         fetch_tests_from_worker(controller);
         return wait_for_message()
       })
       .then(({id}) => clientId = id)
       .then(___ => run_test(controller, clientId, "test_client_navigate_mixed_content"))
       .then(({result, url}) => {
         assert_equals(result, "test_client_navigate_mixed_content");
         assert_equals(