Add app.window.alphaEnabled() and onAlphaEnabledChanged.

chrome/browser/extensions/api/app_window/app_window_api.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 "chrome/browser/extensions/api/app_window/app_window_api.h"
 
 #include "apps/app_window.h"
 #include "apps/app_window_contents.h"
 #include "apps/app_window_registry.h"
 #include "apps/apps_client.h"
@@ skipping 215 matching lines @@
         GetExtension()->location() == extensions::Manifest::COMPONENT) {
       if (options->type == extensions::api::app_window::WINDOW_TYPE_PANEL) {
         create_params.window_type = AppWindow::WINDOW_TYPE_PANEL;
       }
     }
 
     if (!GetFrameOptions(*options, &create_params))
       return false;
 
     if (options->transparent_background.get() &&
+        create_params.frame == AppWindow::FRAME_NONE &&

[Wez, 2014/07/09 22:03:30]

If requesting transparent background requires frame=none then rather than
silently fail, perhaps we should actually return an API error - WDYT?

[jackhou1, 2014/07/10 03:04:18]

Done.

         (GetExtension()->permissions_data()->HasAPIPermission(
              APIPermission::kExperimental) ||
          CommandLine::ForCurrentProcess()->HasSwitch(
              switches::kEnableExperimentalExtensionApis))) {
       create_params.transparent_background = *options->transparent_background;
     }
 
     if (options->hidden.get())
       create_params.hidden = *options->hidden.get();
 
@@ skipping 244 matching lines @@
 
   if (options.frame->as_frame_options->inactive_color.get()) {
     error_ = app_window_constants::kInactiveColorWithoutColor;
     return false;
   }
 
   return true;
 }
 
 }  // namespace extensions