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

chrome/browser/resources/settings/device_page/storage.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-light.html">
 <link rel="import" href="drive_cache_dialog.html">
 <link rel="import" href="../prefs/prefs.html">
 <link rel="import" href="../route.html">
 <link rel="import" href="../settings_shared_css.html">
 
@@ skipping 165 matching lines @@
             </div>
           </div>
         </div>
       </div>
     </div>
     <div class="settings-box" on-tap="onDownloadsTap_" actionable>
       <div class="start">$i18n{storageItemDownloads}</div>
       <div id="downloadsSize" class="storage-size">
         $i18n{storageSizeComputing}
       </div>
-      <button class="icon-external" is="paper-icon-button-light"></button>
+      <button class="icon-external" is="paper-icon-button-light"
+          aria-label="$i18n{storageItemDownloads}"
+          aria-describedby="downloadSize"></button>

[hcarmona, 2017/02/13 17:53:54]

aria-describedby="downloadsSize"

[Dan Beam, 2017/02/13 17:56:18]

Done.

     </div>
     <template is="dom-if" if="[[driveEnabled_]]">
       <div class="settings-box" on-tap="onDriveCacheTap_" actionable>
         <div class="start">$i18n{storageItemDriveCache}</div>
         <div id="driveCacheSize" class="storage-size">
           $i18n{storageSizeComputing}
         </div>
-        <button class="subpage-arrow" is="paper-icon-button-light"></button>
+        <button class="subpage-arrow" is="paper-icon-button-light"
+            aria-label="$i18n{storageItemDriveCache}"
+            aria-describedby="driveSizeCache"></button>
       </div>
     </template>
     <div class="settings-box" on-tap="onBrowsingDataTap_" actionable>
       <div class="start">$i18n{storageItemBrowsingData}</div>
       <div id="browsingDataSize" class="storage-size">
         $i18n{storageSizeComputing}
       </div>
-      <button class="subpage-arrow" is="paper-icon-button-light"></button>
+      <button class="subpage-arrow" is="paper-icon-button-light"
+          aria-label="$i18n{storageItemBrowsingData}"
+          aria-describedby="browsingDataSize"></button>
     </div>
     <template is="dom-if" if="[[androidEnabled_]]">
       <div class="settings-box" on-tap="onAndroidTap_" actionable>
         <div class="start">$i18n{storageItemAndroid}</div>
         <div id="androidSize" class="storage-size">
           $i18n{storageSizeComputing}
         </div>
-        <button class="icon-external" is="paper-icon-button-light"></button>
+        <button class="icon-external" is="paper-icon-button-light"
+            aria-label="$i18n{storageItemAndroid}"
+            aria-describedby="androidSize"></button>
       </div>
     </template>
     <template is="dom-if" if="[[!isGuest_]]">
       <div class="settings-box" on-tap="onOtherUsersTap_" actionable>
         <div class="start">$i18n{storageItemOtherUsers}</div>
         <div id="otherUsersSize" class="storage-size">
           $i18n{storageSizeComputing}
         </div>
-        <button class="subpage-arrow" is="paper-icon-button-light"></button>
+        <button class="subpage-arrow" is="paper-icon-button-light"
+            aria-label="$i18n{storageItemOtherUsers}"
+            aria-describedby="otherUsersSize"></button>
       </div>
     </template>
 
     <settings-drive-cache-dialog id="storageDriveCache">
     </settings-drive-cache-dialog>
   </template>
   <script src="storage.js"></script>
 </dom-module>