MD Settings: reduce complexity and overhead of Languages singleton

chrome/browser/resources/settings/languages_page/manage_languages_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-manage-languages-page' is a sub-page for enabling
  * and disabling languages.
  */
 Polymer({
   is: 'settings-manage-languages-page',
 
   properties: {
     /**
      * Preferences state.
      */
     prefs: {
       type: Object,
       notify: true,
     },
 
     /**
      * @type {!LanguagesModel|undefined}
      */
     languages: {
       type: Object,
       notify: true,
     },
-
-    /** @private {!LanguageHelper} */
-    languageHelper_: Object,
-  },
-
-  /** @override */
-  created: function() {
-     this.languageHelper_ = LanguageHelperImpl.getInstance();
   },
 
   /**
    * @param {!chrome.languageSettingsPrivate.Language} language
    * @param {!Object} change Polymer change object (provided in the HTML so this
    *     gets called whenever languages.enabled.* changes).
    * @return {boolean}
    * @private
    */
   isCheckboxChecked_: function(language, change) {
-    return this.languageHelper_.isLanguageEnabled(language.code);
+    return settings.LanguageHelperImpl.getInstance().isLanguageEnabled(
+        language.code);
   },
 
   /**
    * Determines whether a language must be enabled. If so, the checkbox in the
-   * available languages list should not be changeable.
+   * available languages list should not be changeable. Only applies to
+   * already-enabled languages.
    * @param {!chrome.languageSettingsPrivate.Language} language
    * @param {!Object} change Polymer change object (provided in the HTML so this
    *     gets called whenever languages.enabled.* changes).
    * @return {boolean}
    * @private
    */
   isLanguageRequired_: function(language, change) {
-    // This check only applies to enabled languages.
-    if (!this.languageHelper_.isLanguageEnabled(language.code))
-      return false;
-    return !this.languageHelper_.canDisableLanguage(language.code);
+    var languageHelper = settings.LanguageHelperImpl.getInstance();
+    return languageHelper.isLanguageEnabled(language.code) &&
+        !languageHelper.canDisableLanguage(language.code);
   },
 
   /**
    * Handler for removing a language.
    * @param {!{model: !{item: !LanguageState}}} e
    * @private
    */
   onRemoveLanguageTap_: function(e) {
-    this.languageHelper_.disableLanguage(e.model.item.language.code);
+    settings.LanguageHelperImpl.getInstance().disableLanguage(
+        e.model.item.language.code);
   },
 
   /**
    * Handler for checking or unchecking a language item.
    * @param {!{model: !{item: !chrome.languageSettingsPrivate.Language},
    *           target: !PaperCheckboxElement}} e
    * @private
    */
   onLanguageCheckboxChange_: function(e) {
     var code = e.model.item.code;
     if (e.target.checked)
-      this.languageHelper_.enableLanguage(code);
+      settings.LanguageHelperImpl.getInstance().enableLanguage(code);
     else
-      this.languageHelper_.disableLanguage(code);
+      settings.LanguageHelperImpl.getInstance().disableLanguage(code);
   },
 });