MD Settings/About: Implement update progress percentage

chrome/browser/resources/settings/about_page/about_page.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.
 
 /**
  * @fileoverview 'settings-about-page' contains version and OS related
  * information.
  */
 Polymer({
   is: 'settings-about-page',
@@ skipping 142 matching lines @@
         return this.i18n('aboutUpgradeCheckStarted');
       case UpdateStatus.NEARLY_UPDATED:
 <if expr="chromeos">
         if (this.currentChannel_ != this.targetChannel_)
           return this.i18n('aboutUpgradeSuccessChannelSwitch');
 </if>
         return this.i18n('aboutUpgradeRelaunch');
       case UpdateStatus.UPDATED:
         return this.i18n('aboutUpgradeUpToDate');
       case UpdateStatus.UPDATING:
+        assert(typeof this.currentUpdateStatusEvent_.progress == 'number');
+        var progressPercent = this.currentUpdateStatusEvent_.progress + '%';
+
 <if expr="chromeos">
         if (this.currentChannel_ != this.targetChannel_) {
           return this.i18n('aboutUpgradeUpdatingChannelSwitch',
-              this.i18n(settings.browserChannelToI18nId(this.targetChannel_)));
+              this.i18n(settings.browserChannelToI18nId(this.targetChannel_)),
+              progressPercent);
         }
 </if>
-        return this.i18n('aboutUpgradeUpdating');
+        return this.i18n('aboutUpgradeUpdating', progressPercent);
       default:
         var message = this.currentUpdateStatusEvent_.message;
         return message ?
             parseHtmlSubset('<b>' + message + '</b>').firstChild.innerHTML :
             '';
     }
   },
 
   /**
    * @return {?string}
@@ skipping 109 matching lines @@
     });
   },
 
 <if expr="_google_chrome">
   /** @private */
   onReportIssueTap_: function() {
     this.aboutBrowserProxy_.openFeedbackDialog();
   },
 </if>
 });