Add app.window.alphaEnabled() and onAlphaEnabledChanged.

chrome/browser/ui/views/apps/chrome_native_app_window_views_win.cc

 // 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.
 
 #include "chrome/browser/ui/views/apps/chrome_native_app_window_views_win.h"
 
 #include "apps/app_window.h"
 #include "apps/app_window_registry.h"
 #include "apps/ui/views/app_window_frame_view.h"
 #include "ash/shell.h"
@@ skipping 176 matching lines @@
                                               extension->id());
 
     ShellLinkItemList items;
     items.push_back(link);
     jumplist_updater.AddTasks(items);
   }
 
   // Note that an empty jumplist must still be committed to clear all items.
   jumplist_updater.CommitUpdate();
 }
+
+bool ChromeNativeAppWindowViewsWin::CanHaveTransparentBackground() const {
+  return ui::win::IsAeroGlassEnabled();
+}