Make it so that allow_js_access: false can be used with background pages created by window.open.

chrome/test/data/extensions/api_test/app_background_page/no_js/launch.html

+<!--
+ * 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.
+-->
+<script src="../common/common.js"></script>
+<div style="display:none" id="pageToScriptTunnel"></div>
+<div style="display:none" id="scriptToPageTunnel"></div>
+<script>
+
+window.onload = function() {
+  setupScriptTunnel();
+  var backgroundWindow = window.open('bg.html', 'bg', 'background');
+  if (backgroundWindow) {
+    notifyBackgroundWindowNotNull();
+  }
+}
+
+function notifyBackgroundWindowNotNull() {
+  pageToScriptTunnel.innerText = JSON.stringify(messageData(arguments));
+  pageToScriptTunnel.dispatchEvent(scriptMessageEvent);
+}
+</script>