MD-Settings: Adds an a11y label to most toggle buttons.

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

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-toggle-button/paper-toggle-button.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_action_menu/cr_action_menu.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="../i18n_setup.html">
 <link rel="import" href="../settings_shared_css.html">
 <link rel="import" href="site_settings_behavior.html">
 <link rel="import" href="site_settings_prefs_browser_proxy.html">
 
 <dom-module id="protocol-handlers">
   <template>
     <style include="settings-shared">
       :host {
         display: block;
       }
 
       .site-settings-header {
         -webkit-margin-start: 20px;
         margin-bottom: 15px;
         margin-top: 15px;
       }
     </style>
     <div class="settings-box first two-line">
-      <div class="start secondary">
+      <div id="categoryLabel" class="start secondary">
         [[computeHandlersDescription_(categoryEnabled)]]
       </div>
       <paper-toggle-button id="toggle" checked="{{categoryEnabled}}"
-          on-change="onToggleChange_"></paper-toggle-button>
+          on-change="onToggleChange_" aria-labelledby="categoryLabel">
+      </paper-toggle-button>
     </div>
 
     <template is="dom-repeat" items="[[protocols]]" as="protocol">
       <div class="site-settings-header">[[protocol.protocol]]</div>
 
       <div class="list-frame menu-content vertical-list">
         <template is="dom-repeat" items="[[protocol.handlers]]">
 
           <div class="list-item">
             <div class="favicon-image" style$="[[computeSiteIcon(item.host)]]">
@@ skipping 22 matching lines @@
         $i18n{handlerSetDefault}
       </button>
       <button class="dropdown-item" role="option" on-tap="onRemoveTap_"
           id="removeButton">
         $i18n{handlerRemove}
       </button>
     </dialog>
   </template>
   <script src="protocol_handlers.js"></script>
 </dom-module>