Extract language settings methods into a LanguageHelper interface

chrome/browser/resources/settings/languages_page/language_detail_page.js

 // Copyright 2015 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-language-detail-page' is a sub-page for editing
  * an individual language's settings.
  *
  * @group Chrome Settings Elements
  * @element settings-language-detail-page
@@ skipping 17 matching lines @@
      */
     languages: Object,
 
     /**
      * The language to display the details for.
      * @type {LanguageInfo|undefined}
      */
     detail: Object,
   },
 
+  /** @private {!LanguageHelper} */
+  languageHelper_: LanguageHelperImpl.getInstance(),
+
   ready: function() {
     // In a CrOS multi-user session, the primary user controls the UI language.
     if (this.isSecondaryUser_()) {
       var indicator = this.$.policyIndicator;
       indicator.indicatorType = CrPolicyIndicatorType.PRIMARY_USER;
       indicator.controllingUser = loadTimeData.getString('primaryUserEmail');
     }
 
     // The UI language choice doesn't persist for guests.
     if (cr.isChromeOS &&
         (uiAccountTweaks.UIAccountTweaks.loggedInAsGuest() ||
          uiAccountTweaks.UIAccountTweaks.loggedInAsPublicAccount())) {
       this.$.languageSettings.hidden = true;
     }
   },
 
+<if expr="chromeos or is_win">
   /**
+   * Checks whether the prospective UI language (the pref that indicates what
+   * language to use in Chrome) matches the current language. This pref is only
+   * on Chrome OS and Windows; we don't control the UI language elsewhere.
    * @param {string} languageCode The language code identifying a language.
-   * @param {string} prospectiveUILanguage The chosen UI language.
-   * @return {boolean} True if the given language matches the chosen UI language
-   *     (which may be different from the actual UI language).
+   * @param {string} prospectiveUILanguage The prospective UI language.
+   * @return {boolean} True if the given language matches the prospective UI
+   *     pref (which may be different from the actual UI language).
    * @private
    */
   isProspectiveUILanguage_: function(languageCode, prospectiveUILanguage) {
-    return languageCode == this.$.languages.getProspectiveUILanguage();
+    return languageCode == this.languageHelper_.getProspectiveUILanguage();
   },
 
   /**
    * @param {string} languageCode The language code identifying a language.
    * @param {string} prospectiveUILanguage The prospective UI language.
    * @return {boolean} True if the the given language, the prospective UI
    *     language and the actual language all the same.
    * @private
    */
   isCurrentUILanguage_: function(languageCode, prospectiveUILanguage) {
     return languageCode == prospectiveUILanguage &&
            languageCode == navigator.language;
   },
+</if>
 
    /**
    * @param {string} languageCode The language code identifying a language.
    * @param {string} targetLanguageCode The default translate target language.
    * @return {boolean} True if the language code matches the target language.
    * @private
    */
   isTranslateDisabled_: function(languageCode, targetLanguageCode) {
-    return this.$.languages.convertLanguageCodeForTranslate(languageCode) ==
+    return this.languageHelper_.convertLanguageCodeForTranslate(languageCode) ==
         targetLanguageCode;
   },
 
    /**
    * @param {string} languageCode The language code identifying a language.
    * @param {string} prospectiveUILanguage The prospective UI language.
    * @return {boolean} True if the prospective UI language is set to
    *     |languageCode| but requires a restart to take effect.
    * @private
    */
@@ skipping 38 matching lines @@
     return !translateEnabled || languageCode == 'zh';
   },
 
   /**
    * Handler for changes to the translate checkbox.
    * @param {!{target: !{checked: boolean}}} e
    * @private
    */
   onTranslateEnabledChange_: function(e) {
     if (e.target.checked)
-      this.$.languages.enableTranslateLanguage(this.detail.language.code);
+      this.languageHelper_.enableTranslateLanguage(this.detail.language.code);
     else
-      this.$.languages.disableTranslateLanguage(this.detail.language.code);
+      this.languageHelper_.disableTranslateLanguage(this.detail.language.code);
   },
 
   /**
    * Handler for changes to the UI language toggle button.
    * @param {!{target: !{checked: boolean}}} e
    * @private
    */
   onUILanguageChange_: function(e) {
     if (e.target.checked) {
-      this.$.languages.setUILanguage(this.detail.language.code);
+      this.languageHelper_.setUILanguage(this.detail.language.code);
     } else {
       // Reset the chosen UI language to the actual UI language.
-      this.$.languages.resetUILanguage();
+      this.languageHelper_.resetUILanguage();
     }
   },
 
   /**
    * Handler for the restart button.
    * @private
    */
   onRestartTap_: function() {
     chrome.send('restart');
   },
 });