Bug 1440984 - Stop importing testharness into a support file, r=ato

This isn't a supported behaviour and may be responsible for the observed intermittents.

Differential Revision: https://phabricator.services.mozilla.com/D14959

--HG--
extra : moz-landing-system : lando

testing/web-platform/tests/html/browsers/browsing-the-web/history-traversal/support/window-name-test.sub.html

@@ -1,7 +1,4 @@
-<script src='/resources/testharness.js'></script>
-<script src='/resources/testharnessreport.js'></script>
 <script>
-  setup({explicit_done: true})
   function process_test_result(passed, test_name) {
     if ({{GET[sendmessage]}}) {
       if (window.opener) {
@@ -10,10 +7,11 @@
         parent.postMessage(passed, "*");
       }
     } else {
-      test(function(t) {
-        assert_equals(passed, true);
+      let host = window.opener || parent;
+      host.test(function(t) {
+        host.assert_equals(passed, true);
       }, test_name);
-      done();
+      host.done();
     }
   }