Add setSelection function to automation API.

chrome/test/data/extensions/api_test/automation/tests/tabs/common.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 assertEq = chrome.test.assertEq;
 var assertFalse = chrome.test.assertFalse;
 var assertTrue = chrome.test.assertTrue;
 
 var EventType = chrome.automation.EventType;
 var RoleType = chrome.automation.RoleType;
 var StateType = chrome.automation.StateType;
 
 var rootNode = null;
 var url = '';
 
 function createTab(url, callback) {
   chrome.tabs.create({"url": url}, function(tab) {
     callback(tab);
   });
 }
 
+function listenOnce(node, eventType, callback, capture) {
+  var innerCallback = function(evt) {
+    node.removeEventListener(eventType, innerCallback, capture);
+    callback(evt);
+  };
+  node.addEventListener(eventType, innerCallback, capture);
+}
+
 function setUpAndRunTests(allTests, opt_path) {
   var path = opt_path || 'index.html';
   getUrlFromConfig(path, function(url) {
     createTab(url, function(unused_tab) {
       chrome.automation.getTree(function (returnedRootNode) {
         rootNode = returnedRootNode;
         if (rootNode.docLoaded) {
           chrome.test.runTests(allTests);
           return;
         }
         rootNode.addEventListener('loadComplete', function() {
           chrome.test.runTests(allTests);
         });
       });
     });
   });
 }
 
 function getUrlFromConfig(path, callback) {
   chrome.test.getConfig(function(config) {
     assertTrue('testServer' in config, 'Expected testServer in config');
     url = ('http://a.com:PORT/' + path)
         .replace(/PORT/, config.testServer.port);
     callback(url)
   });
 }