Show data usage on Site Details (MDSettings)

chrome/browser/resources/settings/site_settings/website_usage_private_api.js

+// Copyright 2016 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.
+
+(function() {
+'use strict';
+
+Polymer({
+  is: 'website-usage-private-api',
+
+  properties: {
+    /**
+     * The amount of data used by the given website.
+     */
+    websiteDataUsage: {
+      type: String,
+      notify: true,
+    },
+  },
+
+  attached: function() {
+    settings.WebsiteUsagePrivateApi.websiteUsagePolymerInstance = this;
+  },
+
+  fetchUsageTotal: function(origin) {
+    settings.WebsiteUsagePrivateApi.fetchUsageTotal(origin);
+  },
+});
+})();
+
+cr.define('settings.WebsiteUsagePrivateApi', function() {
+  /**
+   * @type {Object} An instance of the polymer object defined above.
+   * All data will be set here.
+   */
+  websiteUsagePolymerInstance = null;
+
+  /**
+   * Encapsulates the calls between JS and C++ to fetch how much storage the
+   * origin is using.
+   * Will update the data in |websiteUsagePolymerInstance|.
+   */
+  fetchUsageTotal = function(origin) {
+    chrome.send('fetchUsageTotal', [origin]);
+  };
+
+  /**
+   * Callback for when the usage total is known.
+   * @param {string} usage The string showing how much data the given origin
+   *     is using.
+   */
+  returnUsageTotal = function(usage) {
+    var instance = settings.WebsiteUsagePrivateApi.websiteUsagePolymerInstance;
+    if (instance == null) {
+      return;
+    }
+
+    instance.websiteDataUsage = usage;

[michaelpg, 2016/01/25 18:33:54]

shouldn't we check that the origin is still the same?

e.g.: user checks usage data for A.com, user checks usage data for B.com, C++
responds with A.com usage, site details for B.com shows A.com usage

[Finnur, 2016/01/26 15:54:53]

Like so?

[michaelpg, 2016/01/27 06:37:46]

Yeah, but no need to assert -- it's a valid sequence of events, and I think just
ignoring the outdated response is the right thing to do.

[Finnur, 2016/01/27 10:27:26]

Done.

+  };
+
+  return { websiteUsagePolymerInstance: websiteUsagePolymerInstance,
+           fetchUsageTotal: fetchUsageTotal,
+           returnUsageTotal: returnUsageTotal };
+});