Create OOBE screen for Voice Interaction value proposition

chrome/browser/resources/chromeos/login/oobe_screen_voice_interaction_value_prop.js

+// 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.
+
+/**
+ * @fileoverview Oobe Voice Interaction Value Prop screen implementation.
+ */
+
+login.createScreen('VoiceInteractionValuePropScreen',
+    'voice-interaction-value-prop', function() {
+  return {
+
+    /**
+     * Event handler that is invoked just before the screen is shown.
+     * @param {object} data Screen init payload.
+     */

[xiyuan, 2017/06/02 22:12:33]

nit: This can be just 
  /** @override */

for overridden mthods.

[yueli, 2017/06/06 17:38:19]

Done.

+    onBeforeShow: function(data) {
+      var valueView = $('voice-interaction-value-prop-md').
+          getElement('value-prop-view');
+
+      valueView.request.onHeadersReceived.addListener(function(details) {

[xiyuan, 2017/06/02 22:12:33]

Should we use onErrorOccurred to catch all errors ?

+        if (details.statusLine.match(/^HTTP.*404/)) {

[xiyuan, 2017/06/02 22:12:34]

details.statusCode instead of manually parsing. And we only care of 404 ?

+          valueView.src =
+              'https://www.gstatic.com/opa-chromeos/oobe/en/value_proposition.html';

[xc, 2017/06/02 18:53:48]

if the "en" url were also 404, which should never happen, this is going to be an
infinite loop, right?  Let's check for that and show error for now.  Add a TODO
that we will provide some static content later for the final fallback.

[xiyuan, 2017/06/02 22:12:34]

Good point. Please do. The simplest way is to check valueView.src and only set
to "en" url if it is not.

[yueli, 2017/06/06 17:38:19]

Done.

+        }
+      }, {urls: ['<all_urls>']});

[xiyuan, 2017/06/02 22:12:33]

Think we only care about main frame loading problems. We should add
  types: ['main_frame']
to the filter. Otherwise, subframe or image loading failure would cause the
webview to reload.

[yueli, 2017/06/06 17:38:19]

Done.

+
+      var locale = loadTimeData.getString('locale');
+      valueView.src = 'https://www.gstatic.com/opa-chromeos/oobe/' + locale
+          + '/value_proposition.html';
+
+      Oobe.getInstance().headerHidden = true;
+    }
+  };
+});