Add support for transparent background API

chrome/common/extensions/api/app_window.idl

Index: chrome/common/extensions/api/app_window.idl
diff --git a/chrome/common/extensions/api/app_window.idl b/chrome/common/extensions/api/app_window.idl
index ee3c8d5b6fb4f573a33be2a30fa90d9b7d92f110..373f04546cd7ed3fd8d3a4e4fa8c172af12eac0d 100644
--- a/chrome/common/extensions/api/app_window.idl
+++ b/chrome/common/extensions/api/app_window.idl
@@ -221,8 +221,8 @@ namespace app.window {
     [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'.
@@ -348,6 +348,9 @@ namespace app.window {
     // <code>"alwaysOnTopWindows"</code> permission.
     static void setAlwaysOnTop(boolean alwaysOnTop);
 
+    // Does the window allow a transparent background?
+    static boolean alphaEnabled();
+
     // The JavaScript 'window' object for the created child.
     [instanceOf=Window] object contentWindow;
 
@@ -417,6 +420,9 @@ namespace app.window {
     // Fired when the window is fullscreened.
     [nocompile] static void onFullscreened();
 
+    // Fired when the alphaEnabled flag changes.
+    [nocompile] static void onAlphaEnabledChanged();
+
     // Fired when the window is maximized.
     [nocompile] static void onMaximized();