[Chromoting] Enable jscompile for webapp unittests.

remoting/webapp/unittests/menu_button_unittest.js

 // Copyright 2014 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.
 
 (function() {
 
 'use strict';
 
+/** @type {(sinon.Spy|function():void)} */
 var onShow = null;
+/** @type {(sinon.Spy|function():void)} */
 var onHide = null;
+/** @type {remoting.MenuButton} */
 var menuButton = null;
 
 module('MenuButton', {
   setup: function() {
     var fixture = document.getElementById('qunit-fixture');
     fixture.innerHTML =
         '<span class="menu-button" id="menu-button-container">' +
           '<button class="menu-button-activator">Click me</button>' +
           '<ul>' +
             '<li id="menu-option-1">Option 1</li>' +
           '</ul>' +
         '</span>';
-    onShow = sinon.spy();
-    onHide = sinon.spy();
+    onShow = /** @type {(sinon.Spy|function():void)} */ (sinon.spy());
+    onHide = /** @type {(sinon.Spy|function():void)} */ (sinon.spy());
     menuButton = new remoting.MenuButton(
         document.getElementById('menu-button-container'),
-        onShow, onHide);
+        /** @type {function():void} */ (onShow),
+        /** @type {function():void} */ (onHide));
   },
   teardown: function() {
     onShow = null;
     onHide = null;
     menuButton = null;
   }
 });
 
 test('should display on click', function() {
   var menu = menuButton.menu();
@@ skipping 42 matching lines @@
   var style = window.getComputedStyle(element);
   ok(style.backgroundImage == 'none');
   remoting.MenuButton.select(element, true);
   style = window.getComputedStyle(element);
   ok(style.backgroundImage != 'none');
   remoting.MenuButton.select(element, false);
   style = window.getComputedStyle(element);
   ok(style.backgroundImage == 'none');
 });
 
-}());
+}());