About page UI: add confirmation message for release channel switch.

chrome/browser/resources/help/help.js

 // Copyright (c) 2012 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.
 
 <include src="../uber/uber_utils.js">
 
 cr.define('help', function() {
   /**
    * Encapsulated handling of the help page.
    */
@@ skipping 36 matching lines @@
 
       this.maybeSetOnClick_($('promote'), function() {
         chrome.send('promoteUpdater');
       });
       this.maybeSetOnClick_($('relaunch'), function() {
         chrome.send('relaunchNow');
       });
 
       var channelChanger = $('channel-changer');
       if (channelChanger) {
+        this.channelName_ = {
+            'stable-channel': loadTimeData.getString('stable'),
+            'beta-channel': loadTimeData.getString('beta'),
+            'dev-channel': loadTimeData.getString('dev')
+        };
         var self = this;
         channelChanger.onchange = function(event) {
           self.setReleaseChannel_(event.target.value);
         }
       }
 
       // Attempt to update.
       chrome.send('onPageLoaded');
     },
 
@@ skipping 141 matching lines @@
         if (option.value == value)
           option.selected = true;
       }
     },
 
     /**
      * @private
      */
     setReleaseChannel_: function(channel) {
       chrome.send('setReleaseTrack', [channel]);
+      $('channel-change-confirmation').hidden = false;
+      $('channel-change-confirmation').textContent = loadTimeData.getStringF(
+          'channel-changed', this.channelName_[channel]);
     },
 
     /**
      * Sets the value of the "Build Date" field of the "More Info" section.
      * @param {String} buildDate The date of the build.
      * @private
      */
     setBuildDate_: function(buildDate) {
       $('build-date-container').classList.remove('empty');
       $('build-date').textContent = buildDate;
@@ skipping 49 matching lines @@
     HelpPage: HelpPage
   };
 });
 
 /**
  * onload listener to initialize the HelpPage.
  */
 window.onload = function() {
   help.HelpPage.getInstance().initialize();
 };