Language settings: fix focus issues

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

 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.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-checkbox/paper-checkbox.html">
 <link rel="import" href="/languages_page/languages.html">
 <link rel="import" href="/settings_shared_css.html">
 
 <dom-module id="settings-add-languages-dialog">
   <template>
@@ skipping 18 matching lines @@
     <dialog is="cr-dialog" id="dialog">
       <div class="title">$i18n{addLanguagesDialogTitle}</div>
       <div class="body">
         <!-- TODO(michaelpg): Dynamic language search/filtering. -->
         <iron-list class="ripple-padding" scroll-target="[[$$('.body')]]"
             items="[[getAvailableLanguages_(
                 languages.supported, languages.enabled.*)]]">
           <template>
             <paper-checkbox class="list-item" checked="[[willAdd_(item.code)]]"
                 title$="[[item.nativeDisplayName]]"
-                on-change="onLanguageCheckboxChange_">
+                on-change="onLanguageCheckboxChange_"
+                tabindex$="[[tabIndex]]">
               [[item.displayName]]
             </paper-checkbox>
           </template>
         </iron-list>
       </div>
       <div class="button-container">
         <div class="action-buttons">
           <paper-button class="cancel-button" on-tap="onCancelButtonTap_">
             $i18n{cancel}
           </paper-button>
           <paper-button class="action-button" on-tap="onActionButtonTap_"
               disabled="[[disableActionButton_]]">
             $i18n{add}
           </paper-button>
         </div>
       </div>
     </dialog>
   </template>
   <script src="add_languages_dialog.js"></script>
 </dom-module>