Refactor ServiceWorker tests for inclusion in WPT

third_party/WebKit/LayoutTests/http/tests/serviceworker/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('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;
-  return expect_rejection(np.enable())
-      .then(() => expect_rejection(np.disable()))
-      .then(() => expect_rejection(np.setHeaderValue('hi')))
-      .then(() => np.getState())
-      .then(state => expect_navigation_preload_state(
-          state, false, 'true', 'state should be the default'))
-      .then(() => 'PASS')
-      .catch(err => 'FAIL: ' + err);
-}
-
-var resolve_done_promise;
-var done_promise = new Promise(resolve => { resolve_done_promise = resolve; });
-
-// Run the test once the page messages this worker.
-self.addEventListener('message', e => {
-    e.waitUntil(test_before_activation()
-        .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);
-  });