Add tab.IsServiceWorkerReadyOrNotRegist() which tells whether serviceworker registration is finished

telemetry/telemetry/internal/browser/wait_for_serviceworker_registration.js

Index: telemetry/telemetry/internal/browser/wait_for_serviceworker_registration.js
diff --git a/telemetry/telemetry/internal/browser/wait_for_serviceworker_registration.js b/telemetry/telemetry/internal/browser/wait_for_serviceworker_registration.js
new file mode 100644
index 0000000000000000000000000000000000000000..20e645233d984d3eadddd5a4a454891160a21239
--- /dev/null
+++ b/telemetry/telemetry/internal/browser/wait_for_serviceworker_registration.js
@@ -0,0 +1,40 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+'use strict';
+
+/**
+ * @fileoverview This file provides a JavaScript helper function that
+ * determines whether service worker registration has completed.
+ */
+(function() {
+  // Make executing this code idempotent.
+  if (window.__telemetry_queryServiceWorkerState) {
+    return;
+  }
+
+  // These variable is used for detecting and waiting service worker

[falken, 2017/09/05 02:16:45]

"variable is" => "variables are", "waiting" => "waiting for"

+  // registration.
+  let isServiceWorkerRegistered = false;
+  let isServiceWorkerReady = false;
+
+  // Patch navigator.serviceWorker.register

[falken, 2017/09/05 02:16:45]

I'm not familiar with telemetry style, but probably need a '.' at the end of the
sentence.

+  navigator.serviceWorker.originalRegister = navigator.serviceWorker.register;
+  navigator.serviceWorker.register = (name, options = {}) => {
+    isServiceWorkerRegistered = true;
+    navigator.serviceWorker.originalRegister(name, options);
+  };
+
+  navigator.serviceWorker.ready.then(
+      (registration) => { isServiceWorkerReady = true; });
+
+  window.__telemetry_queryServiceWorkerState = () => {
+    // These return string should exactly match strings used in
+    // ServiceWorkerState, in web_contents.py

[falken, 2017/09/05 02:16:44]

ditto with '.'

+    if (!isServiceWorkerRegistered) {
+      return isServiceWorkerReady ? 'unknown state' : 'not registered';

[falken, 2017/09/05 02:16:44]

maybe 'unknown state' => 'error: ready but register() was not called'

I guess we're assuming this won't happen in our test cases. But maybe it'd be
clearer with a string like this.

+    }
+    return isServiceWorkerReady ? 'activated' : 'installing';

[falken, 2017/09/05 02:16:44]

'activated' is slightly misleading since when .ready resolve, the service worker
is the "active" worker but it's not necessarily "activated" yet (yes, very
confusing). It reaches "activated" after it finishes the 'activate' event
handler, and .ready resolves right before that gets dispatched.

I'd prefer:
isServiceWorkerReady ? 'active' : 'installing'

This is more consistent with the properties on ServiceWorkerRegistration:
https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerRegistration

To be really precise, we could say 'installing_or_waiting', but as long as
there's not an 'active' worker, any 'waiting' worker becomes 'active'
immediately. And it seems we don't care about ensuring that the service worker
installed by *this* register() call became active, as long as there's an active
worker we're happy.

+  };
+})();