Add support for transparent background API

apps/ui/views/native_app_window_views.h

 // 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.
 
 #ifndef APPS_UI_VIEWS_NATIVE_APP_WINDOW_VIEWS_H_
 #define APPS_UI_VIEWS_NATIVE_APP_WINDOW_VIEWS_H_
 
 #include "apps/size_constraints.h"
 #include "apps/ui/native_app_window.h"
 #include "base/observer_list.h"
@@ skipping 159 matching lines @@
   // Informs modal dialogs that they need to update their positions.
   void OnViewWasResized();
 
   AppWindow* app_window_;  // Not owned.
   views::WebView* web_view_;
   views::Widget* widget_;
 
   scoped_ptr<SkRegion> draggable_region_;
 
   bool frameless_;
-  bool transparent_background_;
+  bool alpha_enabled_;
   bool resizable_;
   apps::SizeConstraints size_constraints_;
 
   views::UnhandledKeyboardEventHandler unhandled_keyboard_event_handler_;
 
   ObserverList<web_modal::ModalDialogHostObserver> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeAppWindowViews);
 };
 
 }  // namespace apps
 
 #endif  // APPS_UI_VIEWS_NATIVE_APP_WINDOW_VIEWS_H_