MD-Settings A11y: Disable radio list if all options are disabled.

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 252 matching lines @@
       </div>
 
       <div id="encryptionDescription" hidden="[[syncPrefs.passphraseRequired]]"
           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
+        <paper-radio-group disabled$="[[syncPrefs.encryptAllData]]"
             selected="[[selectedEncryptionRadio_(
                 syncPrefs.passphraseTypeIsCustom)]]"
             on-paper-radio-group-changed="onEncryptionRadioSelectionChanged_">
           <paper-radio-button name="encrypt-with-google"
               class="list-item" disabled="[[syncPrefs.encryptAllData]]">
             $i18n{encryptWithGoogleCredentialsLabel}
           </paper-radio-button>
           <paper-radio-button name="encrypt-with-passphrase"
               class="list-item" disabled="[[syncPrefs.encryptAllData]]">
             <template is="dom-if" if="[[syncPrefs.fullEncryptionBody]]">
@@ skipping 37 matching lines @@
                                                          confirmation_)]]">
               $i18n{save}
             </paper-button>
           </div>
         </div>
       </template>
     </div>
   </template>
   <script src="sync_page.js"></script>
 </dom-module>