Add app.window.alphaEnabled() and onAlphaEnabledChanged.

ui/views/widget/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/native_widget_aura.h"
 
 #include "base/bind.h"
 #include "base/strings/string_util.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/aura/client/aura_constants.h"
@@ skipping 673 matching lines @@
 #if !defined(OS_CHROMEOS)
   return DesktopWindowTreeHost::GetNativeTheme(window_);
 #else
   return ui::NativeThemeAura::instance();
 #endif
 }
 
 void NativeWidgetAura::OnRootViewLayout() {
 }
 
+bool NativeWidgetAura::IsTranslucentWindowOpacitySupported() const {
+  return true;
+}
+
 void NativeWidgetAura::RepostNativeEvent(gfx::NativeEvent native_event) {
   OnEvent(native_event);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // NativeWidgetAura, views::InputMethodDelegate implementation:
 
 void NativeWidgetAura::DispatchKeyEventPostIME(const ui::KeyEvent& key) {
   FocusManager* focus_manager = GetWidget()->GetFocusManager();
   delegate_->OnKeyEvent(const_cast<ui::KeyEvent*>(&key));
@@ skipping 447 matching lines @@
   l10n_util::AdjustUIFont(&(ncm.lfCaptionFont));
   base::win::ScopedHFONT caption_font(CreateFontIndirect(&(ncm.lfCaptionFont)));
   return gfx::FontList(gfx::Font(caption_font));
 #else
   return gfx::FontList();
 #endif
 }
 
 }  // namespace internal
 }  // namespace views