Remove app_shell chrome.shell API and ShellAppWindow

extensions/test/data/platform_app/background.js

 // 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.
 
-// Stub for app_shell.
-var createWindow =
-    chrome.shell ? chrome.shell.createWindow : chrome.app.window.create;
-
 chrome.app.runtime.onLaunched.addListener(function() {
-  createWindow('hello.html', {
+  chrome.app.window.create('hello.html', {
     'innerBounds': {
       'width': 400,
       'height': 300
     }
   });
 });