Add the first app_shell_browsertest test.

extensions/test/data/platform_app/world.js

Index: extensions/test/data/platform_app/world.js
diff --git a/chrome/test/data/extensions/platform_apps/ephemeral_apps/dispatch_event/index.js b/extensions/test/data/platform_app/world.js
similarity index 64%
copy from chrome/test/data/extensions/platform_apps/ephemeral_apps/dispatch_event/index.js
copy to extensions/test/data/platform_app/world.js
index dc590d190815d0645476120ece798c9fb5b4db35..9804641fc88c20ec6f08df49d9154a7056ce40da 100644
--- a/chrome/test/data/extensions/platform_apps/ephemeral_apps/dispatch_event/index.js
+++ b/extensions/test/data/platform_app/world.js
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-onload = function() {
-  chrome.test.sendMessage('launched');
+window.onload = function() {
+  console.log('app window opened');
+  chrome.test.notifyPass();
 };