MD Settings/About: Implement update progress percentage

chrome/browser/resources/settings/about_page/about_page.js

Index: chrome/browser/resources/settings/about_page/about_page.js
diff --git a/chrome/browser/resources/settings/about_page/about_page.js b/chrome/browser/resources/settings/about_page/about_page.js
index df86d49102ab781cf575745575e0ef4d4cc2565d..dc61dbb1f5cc056455c123503d309d6fad3174e5 100644
--- a/chrome/browser/resources/settings/about_page/about_page.js
+++ b/chrome/browser/resources/settings/about_page/about_page.js
@@ -160,13 +160,17 @@ Polymer({
       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 ?