Check for warnings when loading extensions in browser tests.

chrome/test/data/extensions/api_test/webnavigation/test_forwardBack.js

 // Copyright (c) 2012 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.
 
-function runTests() {
+onload = function() {
   var getURL = chrome.extension.getURL;
   chrome.tabs.create({"url": "about:blank"}, function(tab) {
     var tabId = tab.id;
 
     chrome.test.runTests([
       // First navigates to a.html which redirects to to b.html which uses
       // history.back() to navigate back to a.html
       function forwardBack() {
         expect([
           { label: "a-onBeforeNavigate",
@@ skipping 85 matching lines @@
                        processId: 0,
                        tabId: 0,
                        timeStamp: 0,
                        url: getURL('forwardBack/a.html') }}],
           [ navigationOrder("a-"), navigationOrder("b-"), navigationOrder("c-"),
             isLoadedBy("b-", "a-"), isLoadedBy("c-", "b-")]);
         chrome.tabs.update(tabId, { url: getURL('forwardBack/a.html') });
       },
     ]);
   });
-}
+};