MD Settings: About page, implementing channel switcher dialog.

chrome/browser/resources/settings/about_page/about_page_browser_proxy.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 A helper object used from the "About" section to interact with
  * the browser.
  */
 
 <if expr="chromeos">
@@ skipping 57 matching lines @@
   function browserChannelToI18nId(channel) {
     switch (channel) {
       case BrowserChannel.BETA: return 'aboutChannelBeta';
       case BrowserChannel.DEV: return 'aboutChannelDev';
       case BrowserChannel.STABLE: return 'aboutChannelStable';
     }
 
     assertNotReached();
   }
 
+  /**
+   * @param {!BrowserChannel} currentChannel
+   * @param {!BrowserChannel} targetChannel
+   * @return {boolean} Whether the target channel is more stable than the
+   *     current channel.
+   */
+  function isTargetChannelMoreStable(currentChannel, targetChannel) {
+    // List of channels in increasing stability order.
+    var channelList = [
+      BrowserChannel.DEV,
+      BrowserChannel.BETA,
+      BrowserChannel.STABLE,
+    ];
+    var currentIndex = channelList.indexOf(currentChannel);
+    var targetIndex = channelList.indexOf(targetChannel);
+    return currentIndex < targetIndex;
+  }
+
   /** @interface */
   function AboutPageBrowserProxy() {}
 
   AboutPageBrowserProxy.prototype = {
     /**
      * Indicates to the browser that the page is ready.
      */
     pageReady: function() {},
 
     /**
@@ skipping 108 matching lines @@
     getRegulatoryInfo: function() {
       return cr.sendWithPromise('getRegulatoryInfo');
     }
 </if>
   };
 
   return {
     AboutPageBrowserProxy: AboutPageBrowserProxy,
     AboutPageBrowserProxyImpl: AboutPageBrowserProxyImpl,
     browserChannelToI18nId: browserChannelToI18nId,
+    isTargetChannelMoreStable: isTargetChannelMoreStable,
   };
 });