Add app.window.alphaEnabled() and onAlphaEnabledChanged.

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.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_x11.h"
 
 #include <X11/extensions/shape.h>
 #include <X11/extensions/XInput2.h>
 #include <X11/Xatom.h>
 #include <X11/Xregion.h>
@@ skipping 813 matching lines @@
   if (xwindow_) {
     x11_capture_.reset();
     native_widget_delegate_->AsWidget()->GetInputMethod()->OnBlur();
   }
 }
 
 bool DesktopWindowTreeHostX11::IsAnimatingClosed() const {
   return false;
 }
 
+bool DesktopWindowTreeHostX11::IsTranslucentWindowOpacitySupported() const {
+  return false;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopWindowTreeHostX11, aura::WindowTreeHost implementation:
 
 ui::EventSource* DesktopWindowTreeHostX11::GetEventSource() {
   return this;
 }
 
 gfx::AcceleratedWidget DesktopWindowTreeHostX11::GetAcceleratedWidget() {
   return xwindow_;
 }
@@ skipping 970 matching lines @@
   if (linux_ui) {
     ui::NativeTheme* native_theme = linux_ui->GetNativeTheme(window);
     if (native_theme)
       return native_theme;
   }
 
   return ui::NativeTheme::instance();
 }
 
 }  // namespace views