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 tree = null;
 
 function createTab(url, callback) {
   chrome.tabs.create({"url": url}, function(tab) {
       chrome.runtime.onMessage.addListener(
         function listener(message, sender) {
           if (!sender.tab)
             return;
           assertEq(tab.id, sender.tab.id);
           assertTrue(message['loaded']);
-          callback();
+          callback(tab);
           chrome.runtime.onMessage.removeListener(listener);
         });
       });
 }
 
 function setUpAndRunTests(allTests) {
+  getUrlFromConfig(function(url) {
+    createTab(url, function(unused_tab) {
+      chrome.automation.getTree(function (returnedTree) {
+        tree = returnedTree;
+        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;
-      chrome.test.runTests(allTests);
-    }
-    createTab(url, function() {
-      chrome.automation.getTree(gotTree);
-    });
+    callback(url)
   });
 }
-