Add the first app_shell_browsertest test.

extensions/test/data/platform_app/background.js

Index: extensions/test/data/platform_app/background.js
diff --git a/chrome/test/data/chromeos/demo_app/js/background.js b/extensions/test/data/platform_app/background.js
similarity index 66%
copy from chrome/test/data/chromeos/demo_app/js/background.js
copy to extensions/test/data/platform_app/background.js
index 0ecb137cda94a67fd11a0469b9304221f0e1ae11..9820db775d97d78046c77841671dc45b2203f926 100644
--- a/chrome/test/data/chromeos/demo_app/js/background.js
+++ b/extensions/test/data/platform_app/background.js
@@ -1,7 +1,11 @@
 // Copyright 2014 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.
-
 chrome.app.runtime.onLaunched.addListener(function() {
-  chrome.app.window.create('html/main.html', {'state': 'fullscreen'});
+  chrome.app.window.create('hello.html', {
+    'bounds': {
+      'width': 400,
+      'height': 300
+    }
+  });
 });