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::CanHaveAlphaEnabled() const {
+  return ui::win::IsAeroGlassEnabled();

[tapted, 2014/07/14 03:30:24]

You could also use widget()->ShouldWindowContentsBeTransparent();

Sadly (I think) it returns `false` on ChromeOS

[jackhou1, 2014/07/14 04:51:03]

ShouldWindowContentsBeTransparent is meant for native frames that have
Aero-style transparency, e.g. browser windows where the tabs are mildly
transparent. I think it's the same mechanism used to get transparent backgrounds
on Aero, but the logic isn't the same, so it's probably better to have a
different method for CanHaveAlphaEnabled.

+}