MD Settings: Factor out some pref manipulation into the PrefsBehavior.

chrome/browser/resources/settings/languages_page/languages.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-languages' provides convenient access to
  * Chrome's language and input method settings.
  *
  * Instances of this element have a 'languages' property, which reflects the
  * current language settings. The 'languages' property is read-only, meaning
@@ skipping 329 matching lines @@
    * Disables the language.
    * @param {string} languageCode
    */
   disableLanguage: function(languageCode) {
     if (!CrSettingsPrefs.isInitialized)
       return;
 
     assert(this.canDisableLanguage(languageCode));
 
     // Remove the language from spell check.
-    this.arrayDelete('prefs.spellcheck.dictionaries.value', languageCode);
+    this.deletePrefListItem('spellcheck.dictionaries', languageCode);
 
     // Remove the language from preferred languages.
     var languageCodes =
         this.getPref(preferredLanguagesPrefName).value.split(',');
     var languageIndex = languageCodes.indexOf(languageCode);
     if (languageIndex == -1)
       return;
     languageCodes.splice(languageIndex, 1);
     chrome.languageSettingsPrivate.setLanguageList(languageCodes);
     this.enableTranslateLanguage(languageCode);
@@ skipping 17 matching lines @@
     return true;
   },
 
   /**
    * Enables translate for the given language by removing the translate
    * language from the blocked languages preference.
    * @param {string} languageCode
    */
   enableTranslateLanguage: function(languageCode) {
     languageCode = this.convertLanguageCodeForTranslate(languageCode);
-    this.arrayDelete('prefs.translate_blocked_languages.value', languageCode);
+    this.deletePrefListItem('translate_blocked_languages', languageCode);
   },
 
   /**
    * Disables translate for the given language by adding the translate
    * language to the blocked languages preference.
    * @param {string} languageCode
    */
   disableTranslateLanguage: function(languageCode) {
-    languageCode = this.convertLanguageCodeForTranslate(languageCode);
-    if (this.getPref('translate_blocked_languages').value
-            .indexOf(languageCode) == -1) {
-      this.push('prefs.translate_blocked_languages.value', languageCode);
-    }
+    this.appendPrefListItem('translate_blocked_languages',
+        this.convertLanguageCodeForTranslate(languageCode));
   },
 
   /**
    * Enables or disables spell check for the given language.
    * @param {string} languageCode
    * @param {boolean} enable
    */
   toggleSpellCheck: function(languageCode, enable) {
     if (!this.initialized_)
       return;
 
     if (enable) {
       var spellCheckPref = this.getPref('spellcheck.dictionaries');
-      if (spellCheckPref.value.indexOf(languageCode) == -1)
-        this.push('prefs.spellcheck.dictionaries.value', languageCode);
+      this.appendPrefListItem('spellcheck.dictionaries', languageCode);
     } else {
-      this.arrayDelete('prefs.spellcheck.dictionaries.value', languageCode);
+      this.deletePrefListItem('spellcheck.dictionaries', languageCode);
     }
   },
 
   /**
    * Converts the language code for translate. There are some differences
    * between the language set the Translate server uses and that for
    * Accept-Language.
    * @param {string} languageCode
    * @return {string} The converted language code.
    */
@@ skipping 74 matching lines @@
    * manually sending a change notification for our 'languages' property (since
    * it's the same object as the singleton's property, but isn't bound by
    * Polymer).
    * @private
    */
   singletonLanguagesChanged_: function(e) {
     // Forward the change notification to the host.
     this.fire(e.type, e.detail, {bubbles: false});
   },
 });