Add support for transparent background API

chrome/common/extensions/api/app_window.idl

 // 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.
 
 // Use the <code>chrome.app.window</code> API to create windows. Windows
 // have an optional frame with title bar and size controls. They are not
 // associated with any Chrome browser windows. See the <a
 // href="https://github.com/GoogleChrome/chrome-app-samples/tree/master/window-state">
 // Window State Sample</a> for a demonstration of these options.
 namespace app.window {
@@ skipping 213 matching lines @@
     //
     // Use of <code>FrameOptions</code> is new in M36.
     (DOMString or FrameOptions)? frame;
 
     // Size and position of the content in the window (excluding the titlebar).
     // If an id is also specified and a window with a matching id has been shown
     // before, the remembered bounds of the window will be used instead.
     [deprecated="Use innerBounds or outerBounds."] ContentBounds? bounds;
 
     // Enable window background transparency.
-    // Only supported in ash. Requires experimental API permission.
-    boolean? transparentBackground;
+    // Only supported in ash. Requires app.window.alpha API permission.
+    boolean? alphaEnabled;
 
     // The initial state of the window, allowing it to be created already
     // fullscreen, maximized, or minimized. Defaults to 'normal'.
     State? state;
 
     // If true, the window will be created in a hidden state. Call show() on
     // the window to show it once it has been created. Defaults to false.
     boolean? hidden;
 
     // If true, the window will be resizable by the user. Defaults to true.
@@ skipping 205 matching lines @@
     // Fired when the window is restored from being minimized or maximized.
     [nocompile] static void onRestored();
 
     // Fired when the window's ability to use alpha transparency changes.
     [nocompile, nodoc] static void onAlphaEnabledChanged();
 
     // Event for testing. Lets tests wait until a window has been shown.
     [nocompile, nodoc] static void onWindowFirstShown();
   };
 };