Refactor ServiceWorker tests for inclusion in WPT

third_party/WebKit/LayoutTests/external/wpt/service-workers/service-worker/navigation-preload/resources/wait-for-activate-worker.js

 // This worker remains in the installing phase so that the
 // navigation preload API can be tested when there is no
 // active worker.
-importScripts('../../../resources/testharness.js');
+importScripts('/resources/testharness.js');
 importScripts('helpers.js');
 
 function expect_rejection(promise) {
   return promise.then(
       () => { return Promise.reject('unexpected fulfillment'); },
       err => { assert_equals('InvalidStateError', err.name); });
 }
 
 function test_before_activation() {
   const np = self.registration.navigationPreload;
@@ skipping 16 matching lines @@
         .then(result => {
             e.source.postMessage(result);
             resolve_done_promise();
           }));
   });
 
 // Don't become the active worker until the test is done.
 self.addEventListener('install', e => {
     e.waitUntil(done_promise);
   });