[Aura] Turns on Window opacity support.

views/widget/native_widget_aura.cc

 // Copyright (c) 2011 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.
 
 #include "views/widget/native_widget_aura.h"
 
 #include "base/bind.h"
 #include "ui/aura/desktop.h"
 #include "ui/aura/event.h"
 #include "ui/aura/window.h"
@@ skipping 378 matching lines @@
 
 void NativeWidgetAura::SetFullscreen(bool fullscreen) {
   fullscreen ? window_->Fullscreen() : window_->Restore();
 }
 
 bool NativeWidgetAura::IsFullscreen() const {
   return window_->show_state() == ui::SHOW_STATE_FULLSCREEN;
 }
 
 void NativeWidgetAura::SetOpacity(unsigned char opacity) {
-  NOTIMPLEMENTED();
+  window_->layer()->SetOpacity(opacity / 255.0);
 }
 
 void NativeWidgetAura::SetUseDragFrame(bool use_drag_frame) {
   NOTIMPLEMENTED();
 }
 
 bool NativeWidgetAura::IsAccessibleWidget() const {
   NOTIMPLEMENTED();
   return false;
 }
@@ skipping 234 matching lines @@
 }
 
 // static
 bool NativeWidgetPrivate::IsMouseButtonDown() {
   NOTIMPLEMENTED();
   return false;
 }
 
 }  // namespace internal
 }  // namespace views