Add app.window.alphaEnabled() and onAlphaEnabledChanged.

ui/views/widget/desktop_aura/desktop_native_widget_aura.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_native_widget_aura.h"
 
 #include "base/bind.h"
 #include "base/debug/trace_event.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/cursor_client.h"
@@ skipping 914 matching lines @@
 
 ui::NativeTheme* DesktopNativeWidgetAura::GetNativeTheme() const {
   return DesktopWindowTreeHost::GetNativeTheme(content_window_);
 }
 
 void DesktopNativeWidgetAura::OnRootViewLayout() const {
   if (content_window_)
     desktop_window_tree_host_->OnRootViewLayout();
 }
 
+bool DesktopNativeWidgetAura::CanHaveAlphaEnabled() const {
+  return content_window_ && desktop_window_tree_host_->CanHaveAlphaEnabled();
+}
+
 void DesktopNativeWidgetAura::RepostNativeEvent(gfx::NativeEvent native_event) {
   OnEvent(native_event);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopNativeWidgetAura, aura::WindowDelegate implementation:
 
 gfx::Size DesktopNativeWidgetAura::GetMinimumSize() const {
   return native_widget_delegate_->GetMinimumSize();
 }
@@ skipping 263 matching lines @@
   if (cursor_reference_count_ == 0) {
     // We are the last DesktopNativeWidgetAura instance, and we are responsible
     // for cleaning up |cursor_manager_|.
     delete cursor_manager_;
     native_cursor_manager_ = NULL;
     cursor_manager_ = NULL;
   }
 }
 
 }  // namespace views