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

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

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/action_link.html">
 <link rel="import" href="chrome://resources/html/action_link_css.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-radio-group/paper-radio-group.html">
 <link rel="import" href="../controls/settings_toggle_button.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="fingerprint_list.html">
 <link rel="import" href="lock_screen_constants.html">
@@ skipping 37 matching lines @@
               pref="{{prefs.settings.enable_quick_unlock_fingerprint}}"
               label="$i18n{lockScreenFingerprintEnable}">
           </settings-toggle-button>
         </div>
         <iron-collapse
             opened="[[prefs.settings.enable_quick_unlock_fingerprint.value]]">
           <div class="settings-box continuation" on-tap="onEditFingerprints_"
               actionable>
             <div class="start">
               $i18n{lockScreenEditFingerprints}
-              <div class="secondary">
+              <div class="secondary" id="lockScreenEditFingerprintsSecondary">
                 $i18n{lockScreenEditFingerprintsDescription}
               </div>
             </div>
-            <button class="subpage-arrow" is="paper-icon-button-light"></button>
+            <button class="subpage-arrow" is="paper-icon-button-light"
+                aria-label="$i18n{lockScreenEditFingerprints}"
+                aria-describedby="lockScreenEditFingerprintsSecondary"></button>
           </div>
         </iron-collapse>
       </template>
 
       <div class="settings-box">
         <settings-toggle-button class="start"
             pref="{{prefs.settings.enable_screen_lock}}"
             label="$i18n{enableScreenlock}">
         </settings-toggle-button>
       </div>
 
       <settings-password-prompt-dialog id="passwordPrompt"
           on-close="onPasswordClosed_" set-modes="{{setModes_}}">
       </settings-password-prompt-dialog>
       <settings-setup-pin-dialog id="setupPin" on-done="onPinSetupDone_"
           set-modes="[[setModes_]]">
       </settings-setup-pin-dialog>
     </div>
   </template>
 
   <script src="lock_screen.js"></script>
 </dom-module>