Add app.window.alphaEnabled() and onAlphaEnabledChanged.

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.h

 // Copyright (c) 2012 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 UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 
 #include <X11/extensions/shape.h>
 #include <X11/Xlib.h>
 
@@ skipping 128 matching lines @@
   virtual bool IsFullscreen() const OVERRIDE;
   virtual void SetOpacity(unsigned char opacity) OVERRIDE;
   virtual void SetWindowIcons(const gfx::ImageSkia& window_icon,
                               const gfx::ImageSkia& app_icon) OVERRIDE;
   virtual void InitModalType(ui::ModalType modal_type) OVERRIDE;
   virtual void FlashFrame(bool flash_frame) OVERRIDE;
   virtual void OnRootViewLayout() OVERRIDE;
   virtual void OnNativeWidgetFocus() OVERRIDE;
   virtual void OnNativeWidgetBlur() OVERRIDE;
   virtual bool IsAnimatingClosed() const OVERRIDE;
+  virtual bool IsTranslucentWindowOpacitySupported() const OVERRIDE;
 
   // Overridden from aura::WindowTreeHost:
   virtual ui::EventSource* GetEventSource() OVERRIDE;
   virtual gfx::AcceleratedWidget GetAcceleratedWidget() OVERRIDE;
   virtual void Show() OVERRIDE;
   virtual void Hide() OVERRIDE;
   virtual gfx::Rect GetBounds() const OVERRIDE;
   virtual void SetBounds(const gfx::Rect& bounds) OVERRIDE;
   virtual gfx::Point GetLocationOnNativeScreen() const OVERRIDE;
   virtual void SetCapture() OVERRIDE;
@@ skipping 180 matching lines @@
   bool urgency_hint_set_;
 
   base::CancelableCallback<void()> delayed_resize_task_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopWindowTreeHostX11);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_