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

chrome/test/data/extensions/api_test/automation/tests/desktop/actions.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 testDoDefault() {
     var firstTextField = findAutomationNode(tree.root,
         function(node) {
           return node.role == 'textField';
         });
     assertTrue(!!firstTextField);
-    firstTextField.addEventListener('focus', function(e) {
+    firstTextField.addEventListener(EventType.focus, function(e) {
       chrome.test.succeed();
     }, true);
     firstTextField.doDefault();
   },
 
   function testFocus() {
     var firstFocusableNode = findAutomationNode(tree.root,
         function(node) {
           return node.role == 'button' && node.state.focusable;
         });
     assertTrue(!!firstFocusableNode);
-    firstFocusableNode.addEventListener('focus', function(e) {
+    firstFocusableNode.addEventListener(EventType.focus, function(e) {
       chrome.test.succeed();
     }, true);
     firstFocusableNode.focus();
   }
 ];
 
 setupAndRunTests(allTests);