Add a basic demo mode browser test.

chrome/test/data/chromeos/demo_app/js/background.js

Index: chrome/test/data/chromeos/demo_app/js/background.js
diff --git a/chrome/test/data/chromeos/demo_app/js/background.js b/chrome/test/data/chromeos/demo_app/js/background.js
new file mode 100644
index 0000000000000000000000000000000000000000..c5d2e2761a9a6e0b0a209db5b5391af62d13de8a
--- /dev/null
+++ b/chrome/test/data/chromeos/demo_app/js/background.js
@@ -0,0 +1,12 @@
+/**
+ * Copyright 2014 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+chrome.app.runtime.onLaunched.addListener(function() {
+  chrome.app.window.create('html/background.html', {'state': 'fullscreen'},
+    function() {
+      chrome.test.sendMessage('launchedDemoApp');
+    });
+});