Add app.window.alphaEnabled() and onAlphaEnabledChanged.

ui/views/widget/widget.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_WIDGET_H_
 #define UI_VIEWS_WIDGET_WIDGET_H_
 
 #include <set>
 #include <stack>
 #include <vector>
@@ skipping 714 matching lines @@
   // Called by our RootView after it has performed a Layout. Used to forward
   // window sizing information to the window server on some platforms.
   void OnRootViewLayout();
 
   // Notification that our owner is closing.
   // NOTE: this is not invoked for aura as it's currently not needed there.
   // Under aura menus close by way of activation getting reset when the owner
   // closes.
   virtual void OnOwnerClosing();
 
+  // Whether the widget can have a transparent background.
+  bool CanHaveAlphaEnabled() const;
+
   // Overridden from NativeWidgetDelegate:
   virtual bool IsModal() const OVERRIDE;
   virtual bool IsDialogBox() const OVERRIDE;
   virtual bool CanActivate() const OVERRIDE;
   virtual bool IsInactiveRenderingDisabled() const OVERRIDE;
   virtual void EnableInactiveRendering() OVERRIDE;
   virtual void OnNativeWidgetActivationChanged(bool active) OVERRIDE;
   virtual void OnNativeFocus(gfx::NativeView old_focused_view) OVERRIDE;
   virtual void OnNativeBlur(gfx::NativeView new_focused_view) OVERRIDE;
   virtual void OnNativeWidgetVisibilityChanging(bool visible) OVERRIDE;
@@ skipping 183 matching lines @@
   bool movement_disabled_;
 
   ScopedObserver<ui::NativeTheme, ui::NativeThemeObserver> observer_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(Widget);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_WIDGET_H_