Allow requesting Automation tree by tabId

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 tree = null;
 
+function createTab(url, callback) {
+  chrome.tabs.create({"url": url}, function(tab) {
+    callback(tab);
+  });
+}
+
 function setUpAndRunTests(allTests) {
+  getUrlFromConfig(function(url) {
+    createTab(url, function(unused_tab) {
+      chrome.automation.getTree(function (returnedTree) {
+        tree = returnedTree;
+        tree.addEventListener('loadComplete', function() {
+          chrome.test.runTests(allTests);
+        });
+      });
+    });
+  });
+}
+
+function getUrlFromConfig(callback) {
   chrome.test.getConfig(function(config) {
     assertTrue('testServer' in config, 'Expected testServer in config');
     var url = 'http://a.com:PORT/index.html'
         .replace(/PORT/, config.testServer.port);
-
-    function gotTree(returnedTree) {
-      tree = returnedTree;
-      tree.addEventListener('loadComplete', function() {
-        chrome.test.runTests(allTests);
-      });
-    }
-    chrome.tabs.create({ 'url': url }, function() {
-      chrome.automation.getTree(gotTree);
-    });
+    callback(url)
   });
 }