MD Settings: label and describe a bunch of subpage/open-in-new buttons

chrome/browser/resources/settings/site_settings/site_data.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout-classes.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="../settings_page/settings_subpage_search.html">
 <link rel="import" href="../settings_shared_css.html">
 <link rel="import" href="cookie_tree_behavior.html">
 <link rel="import" href="site_settings_behavior.html">
 
@@ skipping 24 matching lines @@
       </paper-button>
     </div>
     <div class="list-frame vertical-list">
       <template is="dom-repeat" id="list" items="[[sites]]" filter="showItem_"
           rendered-item-count="{{renderedItemCount}}">
         <div class="list-item two-line" on-tap="onSiteTap_" actionable>
           <div class="favicon-image" style$="[[computeSiteIcon(item.site)]]">
           </div>
           <div class="middle">
             [[item.site]]
-            <div class="secondary">[[item.localData]]</div>
+            <div class="secondary" id="siteSecondary">[[item.localData]]</div>
           </div>
-          <button class="subpage-arrow" is="paper-icon-button-light"></button>
+          <button class="subpage-arrow" is="paper-icon-button-light"
+              aria-label="[[item.site]]"
+              aria-describedby="siteSecondary"></button>
         </div>
       </template>
     </div>
 
     <!-- Confirm Delete dialog -->
     <dialog is="cr-dialog" id="confirmDeleteDialog">
       <div class="title">$i18n{siteSettingsCookieRemoveDialogTitle}</div>
       <div class="body">[[confirmationDeleteMsg_]]</div>
       <div class="button-container">
         <paper-button class="cancel-button" on-tap="onCloseDialog_">
           $i18n{cancel}
         </paper-button>
         <paper-button class="action-button" on-tap="onConfirmDelete_">
           $i18n{siteSettingsCookiesClearAll}
         </paper-button>
       </div>
     </dialog>
   </template>
   <script src="cookie_info.js"></script>
   <script src="cookie_tree_node.js"></script>
   <script src="site_data.js"></script>
 </dom-module>