Add human readable programmatic enum name/values to chrome.automation.

chrome/test/data/extensions/api_test/automation/tests/tabs/location.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.
 
 var allTests = [
   function testLocation() {
     function assertOkButtonLocation(event) {
       var okButton = tree.root.firstChild().firstChild();
       assertTrue('location' in okButton);
       assertEq({left:100, top: 200, width: 300, height: 400},
                okButton.location);
       chrome.test.succeed();
     };
 
     var okButton = tree.root.firstChild().firstChild();
     assertTrue('location' in okButton, 'no location in okButton');
     assertTrue('left' in okButton.location, 'no left in location');
     assertTrue('top' in okButton.location, 'no top in location');
     assertTrue('height' in okButton.location, 'no height in location');
     assertTrue('width' in okButton.location, 'no width in location');
 
-    tree.root.addEventListener('childrenChanged', assertOkButtonLocation);
+    tree.root.addEventListener(
+        EventType.childrenChanged, assertOkButtonLocation);
     chrome.tabs.executeScript({ 'code':
           'document.querySelector("button")' +
           '.setAttribute("style", "position: absolute; left: 100; top: 200; ' +
           'width: 300; height: 400;");' });
   }
 ];
 
 setUpAndRunTests(allTests);