Check for warnings when loading extensions in browser tests.

chrome/test/data/extensions/api_test/webnavigation/test_prerender.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;
   var URL_LOAD =
       "http://127.0.0.1:PORT/files/prerender/prerender_loader.html";
   var URL_TARGET =
       "http://127.0.0.1:PORT/files/prerender/prerender_page.html";
   chrome.tabs.create({"url": "about:blank"}, function(tab) {
     var tabId = tab.id;
     chrome.test.getConfig(function(config) {
       var fixPort = function(url) {
         return url.replace(/PORT/g, config.testServer.port);
@@ skipping 73 matching lines @@
             [ navigationOrder("a-"),
               navigationOrder("b-"),
               [ "a-onCompleted", "b-onCompleted", "onTabReplaced" ]]);
 
           // Notify the api test that we're waiting for the user.
           chrome.test.notifyPass();
         },
       ]);
     });
   });
-}
+};