[CrOS Tether] Add tether settings section to the MD settings page.

chrome/browser/resources/settings/internet_page/internet_subpage.js

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview Polymer element for displaying information about WiFi,
  * WiMAX, or virtual networks.
  */
 
 /** @typedef {chrome.networkingPrivate.DeviceStateProperties} */
@@ skipping 236 matching lines @@
 
   /**
    * @param {!DeviceStateProperties} deviceState
    * @return {string}
    * @private
    */
   getToggleA11yString_: function(deviceState) {
     if (!this.enableToggleIsVisible_(deviceState))
       return '';
     switch (deviceState.Type) {
+      case CrOnc.Type.TETHER:
+        return this.i18n('internetToggleTetherA11yLabel');
       case CrOnc.Type.CELLULAR:
         return this.i18n('internetToggleMobileA11yLabel');
       case CrOnc.Type.WI_FI:
         return this.i18n('internetToggleWiFiA11yLabel');
       case CrOnc.Type.WI_MAX:
         return this.i18n('internetToggleWiMAXA11yLabel');
     }
     assertNotReached();
     return '';
   },
@@ skipping 163 matching lines @@
 
   /**
    * @param {*} lhs
    * @param {*} rhs
    * @return {boolean}
    */
   isEqual_: function(lhs, rhs) {
     return lhs === rhs;
   },
 });