[sensors] Add Permission guard to the generic sensor apis.

third_party/WebKit/LayoutTests/http/tests/resources/permissions-helper.js

 // This file provides a PermissionsHelper object which can be used by
 // LayoutTests using testRunner to handle permissions. The methods in the object
 // return promises so can be used to write idiomatic, race-free code.
 //
 // The current available methods are:
 // - setPermission: given a permission name (known by testRunner) and a state,
 // it will set the permission to the specified state and resolve the promise
 // when done.
 // Example:
 // PermissionsHelper.setPermission('geolocation', 'prompt').then(runTest);
 "use strict";
 
 var PermissionsHelper = (function() {
   function nameToObject(permissionName) {
     switch (permissionName) {
       case "midi":
         return {name: "midi"};
       case "midi-sysex":
         return {name: "midi", sysex: true};
       case "push-messaging":
         return {name: "push", userVisibleOnly: true};
       case "notifications":
         return {name: "notifications"};
       case "geolocation":
         return {name: "geolocation"};
       case "background-sync":
         return {name: "background-sync"};
+      case 'sensors':
+        return {name: 'sensors'};
       default:
         throw "Invalid permission name provided";
     }
   }
 
   return {
     setPermission: function(name, state) {
       return new Promise(function(resolver, reject) {
         navigator.permissions.query(nameToObject(name)).then(function(result) {
             if (result.state == state) {
                 resolver()
                 return;
             }
 
             result.onchange = function() {
                 result.onchange = null;
                 resolver();
             };
 
             testRunner.setPermission(name, state, location.origin, location.origin);
         });
       });
     }
   }
 })();