Add app.window.alphaEnabled() and onAlphaEnabledChanged.

ui/views/widget/native_widget_mac.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 UI_VIEWS_WIDGET_NATIVE_WIDGET_MAC_H_
 #define UI_VIEWS_WIDGET_NATIVE_WIDGET_MAC_H_
 
 #include "ui/gfx/native_widget_types.h"
 #include "ui/views/widget/native_widget_private.h"
 
@@ skipping 90 matching lines @@
   virtual void ClearNativeFocus() OVERRIDE;
   virtual gfx::Rect GetWorkAreaBoundsInScreen() const OVERRIDE;
   virtual Widget::MoveLoopResult RunMoveLoop(
       const gfx::Vector2d& drag_offset,
       Widget::MoveLoopSource source,
       Widget::MoveLoopEscapeBehavior escape_behavior) OVERRIDE;
   virtual void EndMoveLoop() OVERRIDE;
   virtual void SetVisibilityChangedAnimationsEnabled(bool value) OVERRIDE;
   virtual ui::NativeTheme* GetNativeTheme() const OVERRIDE;
   virtual void OnRootViewLayout() const OVERRIDE;
+  virtual bool IsTranslucentWindowOpacitySupported() const OVERRIDE;
   virtual void RepostNativeEvent(gfx::NativeEvent native_event) OVERRIDE;
 
  protected:
   internal::NativeWidgetDelegate* delegate() { return delegate_; }
 
  private:
   friend class test::MockNativeWidgetMac;
 
   internal::NativeWidgetDelegate* delegate_;
   scoped_ptr<BridgedNativeWidget> bridge_;
 
   Widget::InitParams::Ownership ownership_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeWidgetMac);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_NATIVE_WIDGET_MAC_H_