Add app.window.alphaEnabled() and onAlphaEnabledChanged.

ui/views/widget/desktop_aura/desktop_window_tree_host_win.cc

 // 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.
 
 #include "ui/views/widget/desktop_aura/desktop_window_tree_host_win.h"
 
 #include "base/win/metro.h"
 #include "third_party/skia/include/core/SkPath.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/aura/client/aura_constants.h"
@@ skipping 347 matching lines @@
   message_handler_->EndMoveLoop();
 }
 
 void DesktopWindowTreeHostWin::SetVisibilityChangedAnimationsEnabled(
     bool value) {
   message_handler_->SetVisibilityChangedAnimationsEnabled(value);
   content_window_->SetProperty(aura::client::kAnimationsDisabledKey, !value);
 }
 
 bool DesktopWindowTreeHostWin::ShouldUseNativeFrame() const {
-  return ui::win::IsAeroGlassEnabled();
+  return IsTranslucentWindowOpacitySupported();
 }
 
 bool DesktopWindowTreeHostWin::ShouldWindowContentsBeTransparent() const {
   // If the window has a native frame, we assume it is an Aero Glass window, and
   // is therefore transparent. Note: This is not equivalent to calling
   // IsAeroGlassEnabled, because ShouldUseNativeFrame is overridden in a
   // subclass.
   return ShouldUseNativeFrame();
 }
 
@@ skipping 41 matching lines @@
   // HWNDMessageHandler will perform the proper updating on its own.
 }
 
 void DesktopWindowTreeHostWin::OnNativeWidgetBlur() {
 }
 
 bool DesktopWindowTreeHostWin::IsAnimatingClosed() const {
   return pending_close_;
 }
 
+bool DesktopWindowTreeHostWin::IsTranslucentWindowOpacitySupported() const {
+  return ui::win::IsAeroGlassEnabled();
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopWindowTreeHostWin, WindowTreeHost implementation:
 
 ui::EventSource* DesktopWindowTreeHostWin::GetEventSource() {
   return this;
 }
 
 gfx::AcceleratedWidget DesktopWindowTreeHostWin::GetAcceleratedWidget() {
   return message_handler_->hwnd();
 }
@@ skipping 502 matching lines @@
 
 // static
 DesktopWindowTreeHost* DesktopWindowTreeHost::Create(
     internal::NativeWidgetDelegate* native_widget_delegate,
     DesktopNativeWidgetAura* desktop_native_widget_aura) {
   return new DesktopWindowTreeHostWin(native_widget_delegate,
                                       desktop_native_widget_aura);
 }
 
 }  // namespace views