No longer start BG mode until a BackgroundContents is loaded

chrome/test/data/extensions/api_test/app_background_page/basic_open/content_script.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.
+var scriptMessageEvent = document.createEvent("Event");
+scriptMessageEvent.initEvent('scriptMessage', true, true);
+
+var pageToScriptTunnel = document.getElementById("pageToScriptTunnel");
+pageToScriptTunnel.addEventListener("scriptMessage", function() {
+  var data = JSON.parse(pageToScriptTunnel.innerText);
+  chrome.extension.sendRequest(data);
+});
+
+chrome.extension.onRequest.addListener(function(request) {
+  var scriptToPageTunnel = document.getElementById("scriptToPageTunnel");
+  scriptToPageTunnel.innerText = JSON.stringify(request);
+  scriptToPageTunnel.dispatchEvent(scriptMessageEvent);
+});