[Chromoting] Enable jscompile for webapp unittests.

remoting/webapp/js_proto/test_proto.js

 // Copyright 2015 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.
 
 // This file contains various hacks needed to inform JSCompiler of various
 // test-specific properties and methods. It is used only with JSCompiler to
 // verify the type-correctness of our code.
 
 /** @suppress {duplicate} */
 var browserTest = browserTest || {};
 
-/** @suppress {duplicate} */
-var sinon = sinon || {};
-
 /** @interface */
 browserTest.TestableClass = function() {};
 
 /** @param {*} data */
 browserTest.TestableClass.prototype.run = function(data) {};
 
-sinon.spy = function() {};
 
 /** @constructor */
 window.DomAutomationControllerMessage = function() {
   /** @type {boolean} */
   this.succeeded = false;
   /** @type {string} */
   this.error_message = '';
   /** @type {string} */
   this.stack_trace = '';
 };
 
 /** @constructor */
 window.DomAutomationController = function() {};
 
 /** @param {string} json A stringified DomAutomationControllerMessage. */
 window.DomAutomationController.prototype.send = function(json) {};