Enable chrome.automation.getDesktop on all aura platforms.

chrome/test/data/extensions/api_test/automation/tests/desktop/load_tabs.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 getAllWebViews() {
   function findAllWebViews(node, nodes) {
     if (node.role == chrome.automation.RoleType.webView)
       nodes.push(node);
 
     var children = node.children;
     for (var i = 0; i < children.length; i++) {
       var child = findAllWebViews(children[i], nodes);
     }
   }
 
   var webViews = [];
   findAllWebViews(rootNode, webViews);
   return webViews;
 };
 
 var allTests = [
   function testLoadTabs() {
     var webViews = getAllWebViews();
     assertEq(2, webViews.length);
-
-    // Test spins up more quickly than the load; listen for the childrenChanged
-    // event.
-    function childrenChangedListener(evt) {
-      var subroot = webViews[1].firstChild;
-      assertEq(evt.target, subroot.parent);
-      assertEq(subroot, subroot.parent.children[0]);
-
-      var button = subroot.firstChild.firstChild;
-      assertEq(chrome.automation.RoleType.button, button.role);
-
-      var input = subroot.firstChild.lastChild.previousSibling;
-      assertEq(chrome.automation.RoleType.textField, input.role);
-      webViews[1].removeEventListener(
-          chrome.automation.EventType.childrenChanged,
-          childrenChangedListener), true;
-      chrome.test.succeed();
-    }
-    webViews[1].addEventListener(
-        chrome.automation.EventType.childrenChanged,
-        childrenChangedListener,
-        true);
+    var subroot = webViews[1].firstChild;
+    assertEq(webViews[1], subroot.parent);
+    assertEq(subroot, subroot.parent.children[0]);
+    var button = subroot.firstChild.firstChild;
+    assertEq(chrome.automation.RoleType.button, button.role);
+    var input = subroot.firstChild.lastChild.previousSibling;
+    assertEq(chrome.automation.RoleType.textField, input.role);
+    chrome.test.succeed();
   },
 
   function testSubevents() {
     var button = null;
     var webViews = getAllWebViews();
     var subroot = webViews[1].firstChild;
 
     rootNode.addEventListener(chrome.automation.EventType.focus,
         function(evt) {
           assertEq(button, evt.target);
           chrome.test.succeed();
         },
         false);
 
     button = subroot.firstChild.firstChild;
     button.focus();
   }
 ];
 
 setupAndRunTests(allTests,
                  '<button>alpha</button><input type="text">hello</input>');