Add app.window.alphaEnabled() and onAlphaEnabledChanged.

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 b08037bf327bddf1dfbb1ba6e508493e54cff19d..26922d7f68626b19a7735da8f8adda757baf79d2 100644
--- a/chrome/common/extensions/api/app_window.idl
+++ b/chrome/common/extensions/api/app_window.idl
@@ -351,6 +351,10 @@ namespace app.window {
     // <code>"alwaysOnTopWindows"</code> permission.
     static void setAlwaysOnTop(boolean alwaysOnTop);
 
+    // Can the window use alpha transparency?
+    // TODO(jackhou): Document this properly before going to stable.
+    [nodoc] static boolean alphaEnabled();
+
     // The JavaScript 'window' object for the created child.
     [instanceOf=Window] object contentWindow;
 
@@ -433,6 +437,9 @@ namespace app.window {
     // 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();
   };