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

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

 <link rel="import" href="chrome://resources/cr_elements/cr_action_menu/cr_action_menu.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="../icons.html">
 <link rel="import" href="../route.html">
 <link rel="import" href="../settings_shared_css.html">
@@ skipping 51 matching lines @@
           <div class="list-item">
             <div class="start layout horizontal center" on-tap="onOriginTap_"
                 actionable$="[[enableSiteSettings_]]">
               <div class="favicon-image"
                   style$="[[computeSiteIcon(item.origin)]]">
               </div>
               <div class="middle">
                 <div class="selectable">[[item.displayName]]</div>
 
                 <!-- This div must not contain extra whitespace. -->
-                <div class="selectable secondary"
+                <div class="selectable secondary" id="siteDescription"
                     >[[computeSiteDescription_(item)]]</div>
               </div>
             </div>
 
             <template is="dom-if" if="[[!!computeIconControlledBy_(item)]]">
               <iron-icon icon="[[computeIconControlledBy_(item)]]"></iron-icon>
             </template>
 
             <paper-icon-button id="dots" icon="cr:more-vert"
                 hidden="[[isActionMenuHidden_(item.source)]]"
                 on-tap="onShowActionMenuTap_">
             </paper-icon-button>
             <template is="dom-if" if="[[enableSiteSettings_]]">
               <div on-tap="onOriginTap_" actionable>
-                <button class="subpage-arrow" is="paper-icon-button-light">
-                </button>
+                <button class="subpage-arrow" is="paper-icon-button-light"
+                    aria-label="[[item.displayName]]"
+                    aria-describedby="siteDescription"></button>
               </div>
             </template>
           </div>
         </template>
       </div>
     </div>
   </template>
   <script src="site_list.js"></script>
 </dom-module>