[Aura] Turns on Window opacity support.

ui/aura/window.h

Index: ui/aura/window.h
diff --git a/ui/aura/window.h b/ui/aura/window.h
index 57ea1ea251b8c8aac74a5354da3db32d5139aec5..abfad2c33c1f63bf9e5139bf2cf69955d9e1a83d 100644
--- a/ui/aura/window.h
+++ b/ui/aura/window.h
@@ -252,6 +252,9 @@ class AURA_EXPORT Window : public ui::LayerDelegate {
   // Returns true if this window is fullscreen or contains a fullscreen window.
   bool IsOrContainsFullscreenWindow() const;
 
+  // Sets the opacity of the window.
+  void SetOpacity(unsigned char opacity);
+
   // Returns an animation configured with the default duration. All animations
   // should use this. Caller owns returned value.
   static ui::Animation* CreateDefaultAnimation();