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..0d4516cf0f0b7224bcc0dfc3a4e6a8bf136b34a9
--- /dev/null
+++ b/chrome/test/data/chromeos/demo_app/js/background.js
@@ -0,0 +1,14 @@
+/**
+ * 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() {
+  console.log('Demo app launched.');

[xiyuan, 2014/03/20 21:59:44]

nit: This might not be needed though since no one would read them. :)

[rkc, 2014/03/20 22:04:45]

Done.

+  chrome.app.window.create('html/background.html', {'state': 'fullscreen'},
+    function() {
+      console.log('Demo app window created.');
+      chrome.test.sendMessage('launchedDemoApp');
+    });
+});