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

chrome/browser/resources/settings/people_page/sync_page.html

 <link rel="import" href="chrome://resources/html/i18n_behavior.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-a11y-keys/iron-a11y-keys.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-toggle-button/paper-toggle-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-input/paper-input.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-radio-button/paper-radio-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-radio-group/paper-radio-group.html">
 <link rel="import" href="sync_browser_proxy.html">
@@ skipping 167 matching lines @@
               disabled="[[shouldPaymentsCheckboxBeDisabled_(
                   syncPrefs.syncAllDataTypes, syncPrefs.autofillSynced)]]">
           </paper-toggle-button>
         </div>
       </div>
 
       <div class="settings-box two-line" actionable
           on-tap="onManageSyncedDataTap_">
         <div class="start">
           $i18n{manageSyncedDataTitle}
-          <div class="secondary">$i18n{manageSyncedDataDescription}</div>
+          <div class="secondary" id="manageSyncedDataSecondary">
+            $i18n{manageSyncedDataDescription}
+          </div>
         </div>
-        <button class="icon-external" is="paper-icon-button-light"></button>
+        <button class="icon-external" is="paper-icon-button-light"
+            aria-label="$i18n{manageSyncedDataTitle}"
+            aria-describedby="manageSyncedDataSecondary"></button>
       </div>
 
       <div class="settings-box two-line single-column">
         <div>$i18n{encryptionOptionsTitle}</div>
         <div class="secondary">$i18n{syncDataEncryptedText}</div>
       </div>
 
       <div id="encryptionRadioGroupContainer" class="list-frame"
           hidden="[[syncPrefs.passphraseRequired]]">
         <paper-radio-group
@@ skipping 78 matching lines @@
           </div>
           <div id="passphraseRecoverHint" class="list-item">
             <span>$i18nRaw{passphraseRecover}</span>
           </div>
         </div>
       </template>
     </div>
   </template>
   <script src="sync_page.js"></script>
 </dom-module>