Implement initial chrome.browserAction.openPopup API.

chrome/test/data/extensions/api_test/browser_action/open_popup/open_popup_succeeds.js

+// Copyright (c) 2013 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.
+
+// Open a popup then return control to the ApiTest.
+// The ApiTest can reply to the ready message to request another popup to open.
+chrome.browserAction.openPopup(function(popupWindow) {
+  chrome.test.assertTrue(!!popupWindow);
+  chrome.test.notifyPass();
+  chrome.test.sendMessage('ready', function() {
+    chrome.browserAction.openPopup(function(popupWindow2) {
+      chrome.test.assertTrue(!!popupWindow2);
+      chrome.test.succeed();
+    });
+  });
+});