Add skeleton plumbing for serial API. No functionality yet.

chrome/test/data/extensions/api_test/serial/api/background.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 testSerial = function() {
+  var onClose = function(result) {
+    chrome.test.assertTrue(result);
+    chrome.test.succeed();
+  }
+
+  var onOpen = function(connectionInfo) {
+    var connectionId = connectionInfo.connectionId;
+    chrome.test.assertTrue(connectionId > 0);
+    chrome.experimental.serial.close(connectionId, onClose);
+  }
+
+  chrome.experimental.serial.open("/dev/null", onOpen);
+};
+
+chrome.test.runTests([testSerial]);