Service worker: Add self.serviceWorker to ServiceWorkerGlobalScope

- In the previous code, the expiration time was set to null
  so that remaining_timeout() was negative during initial script
  evaluation so that calling self.serviceWorker.postMessage() would fail.
  This CL sets max_request_expiration_time properly
  in ServiceWorkerVersion::StartWorkerInternal().
- Add and fix unittests about expiration time.
- Fix the expected.txt properly.
- In spec, service worker's initial state should be parsed.
  https://w3c.github.io/ServiceWorker/#service-worker-concept

Link to the Chrome Platform Status: https://chromestatus.com/feature/6678900060979200

Bug: 977496
Change-Id: I4f8368e165fb84304b49519ed43d7b21d5ec756d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1819091
Reviewed-by: Kinuko Yasuda <[email protected]>
Reviewed-by: Kent Tamura <[email protected]>
Reviewed-by: Matt Falkenhagen <[email protected]>
Reviewed-by: Makoto Shimazu <[email protected]>
Commit-Queue: Yuta Kasai <[email protected]>
Cr-Commit-Position: refs/heads/master@{#702788}

Author: Yang-33

service-workers/service-worker/global-serviceworker.https.any.js

@@ -17,7 +17,7 @@ async_test((t) => {
   assert_true('serviceWorker' in self, 'self.serviceWorker exists');
   serviceWorker.postMessage({ messageTest: true });
 
-  // The rest of the rest runs once we receive the above message.
+  // The rest of the test runs once this receives the above message.
   addEventListener('message', t.step_func((event) => {
     // Ignore unrelated messages.
     if (!event.data.messageTest) return;