Add app.window.alphaEnabled() and onAlphaEnabledChanged.

chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h

 // Copyright 2013 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 CHROME_BROWSER_UI_COCOA_APPS_NATIVE_APP_WINDOW_COCOA_H_
 #define CHROME_BROWSER_UI_COCOA_APPS_NATIVE_APP_WINDOW_COCOA_H_
 
 #import <Cocoa/Cocoa.h>
 #include <vector>
 
@@ skipping 117 matching lines @@
   virtual void UpdateDraggableRegions(
       const std::vector<extensions::DraggableRegion>& regions) OVERRIDE;
   virtual SkRegion* GetDraggableRegion() OVERRIDE;
   virtual void HandleKeyboardEvent(
       const content::NativeWebKeyboardEvent& event) OVERRIDE;
   virtual bool IsFrameless() const OVERRIDE;
   virtual bool HasFrameColor() const OVERRIDE;
   virtual SkColor ActiveFrameColor() const OVERRIDE;
   virtual SkColor InactiveFrameColor() const OVERRIDE;
   virtual gfx::Insets GetFrameInsets() const OVERRIDE;
+  virtual bool CanHaveTransparentBackground() const OVERRIDE;
 
   // These are used to simulate Mac-style hide/show. Since windows can be hidden
   // and shown using the app.window API, this sets is_hidden_with_app_ to
   // differentiate the reason a window was hidden.
   virtual void ShowWithApp() OVERRIDE;
   virtual void HideWithApp() OVERRIDE;
   virtual void UpdateShelfMenu() OVERRIDE;
   virtual gfx::Size GetContentMinimumSize() const OVERRIDE;
   virtual gfx::Size GetContentMaximumSize() const OVERRIDE;
   virtual void SetContentSizeConstraints(const gfx::Size& min_size,
@@ skipping 63 matching lines @@
   std::vector<extensions::DraggableRegion> draggable_regions_;
 
   // The Extension Command Registry used to determine which keyboard events to
   // handle.
   scoped_ptr<ExtensionKeybindingRegistryCocoa> extension_keybinding_registry_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeAppWindowCocoa);
 };
 
 #endif  // CHROME_BROWSER_UI_COCOA_APPS_NATIVE_APP_WINDOW_COCOA_H_