Settings Rewrite: Restore id of default id to 'main' from ''.

chrome/browser/resources/settings/languages_page/languages_page.html

 <link rel="import" href="chrome://resources/polymer/v1_0/polymer/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icons/iron-icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-item/paper-item.html">
 <link rel="import" href="chrome://resources/html/assert.html">
 <link rel="import" href="chrome://resources/html/cr.html">
 <link rel="import" href="chrome://md-settings/settings_page/settings_animated_pages.html">
 <link rel="import" href="chrome://md-settings/settings_page/settings_subheader.html">
 <link rel="import" href="language_detail_page.html">
 <link rel="import" href="languages.html">
 <link rel="import" href="manage_languages_page.html">
 
 <dom-module id="cr-settings-languages-page">
   <link rel="import" type="css"
       href="chrome://md-settings/settings_page/settings_page.css">
   <link rel="import" type="css" href="languages_page.css">
   <template>
     <cr-settings-languages id="languages" languages="{{languages}}">
     </cr-settings-languages>
     <settings-animated-pages id="pages" current-route="{{currentRoute}}"
         section="languages">
-      <neon-animatable id="">
+      <neon-animatable id="main">
         <h2 i18n-content="languagesListTitle"></h2>
         <div class="item-list">
           <array-selector id="languageSelector" selected="{{detailLanguage}}"
               items="{{languages.enabledLanguages}}"></array-selector>
           <template is="dom-repeat" items="{{languages.enabledLanguages}}">
             <paper-item on-tap="onLanguageTap_">
               <div class="flex" title="[[item.language.nativeDisplayName]]"
                   >[[item.language.displayName]]</div>
               <iron-icon icon="done"
                   hidden$="[[!isUILanguage_(item.language.code, prefs.intl.app_locale.value)]]">
@@ skipping 51 matching lines @@
             page-title="[[detailLanguage.language.displayName]]">
         </settings-subheader>
         <settings-language-detail-page id="languageDetailPage"
             prefs="{{prefs}}" detail="[[detailLanguage]]">
         </settings-language-detail-page>
       </neon-animatable>
     </settings-animated-pages>
   </template>
   <script src="languages_page.js"></script>
 </dom-module>