Add app.window.alphaEnabled() and onAlphaEnabledChanged.

ui/views/widget/native_widget_mac.mm

 // Copyright 2014 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_mac.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_nsobject.h"
@@ skipping 404 matching lines @@
 }
 
 ui::NativeTheme* NativeWidgetMac::GetNativeTheme() const {
   return ui::NativeTheme::instance();
 }
 
 void NativeWidgetMac::OnRootViewLayout() const {
   NOTIMPLEMENTED();
 }
 
+bool NativeWidgetMac::IsTranslucentWindowOpacitySupported() const {

[sky, 2014/07/17 15:52:32]

Does mac really not support translucent windows?

[tapted, 2014/07/18 00:22:28]

It does, but the ubercompositor setup that will be used on mac currently doesn't
- I'm still tracking down where the alpha channel is getting lost [WIP:
crrev.com/283053002]. We will also need to ensure that the way transparent-pixel
hit-testing is accomplished on Mac ticks all the security boxes before allowing
packaged AppWindows to use it.

+  return false;
+}
+
 void NativeWidgetMac::RepostNativeEvent(gfx::NativeEvent native_event) {
   NOTIMPLEMENTED();
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // Widget, public:
 
 bool Widget::ConvertRect(const Widget* source,
                          const Widget* target,
                          gfx::Rect* rect) {
@@ skipping 86 matching lines @@
 }
 
 // static
 gfx::FontList NativeWidgetPrivate::GetWindowTitleFontList() {
   NOTIMPLEMENTED();
   return gfx::FontList();
 }
 
 }  // namespace internal
 }  // namespace views