Get rid of [Callback] extended attribute for parameters in IDL files

Source/core/css/FontLoader.idl

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 25 matching lines @@
 ] interface FontLoader {
 
     attribute EventListener onloading;
     attribute EventListener onloadingdone;
     attribute EventListener onloadstart;
     attribute EventListener onload;
     attribute EventListener onerror;
 
     boolean checkFont(DOMString font, [Default=NullString] optional DOMString text);
     void loadFont(Dictionary params);
-    void notifyWhenFontsReady([Callback] VoidCallback callback);
+    void notifyWhenFontsReady(VoidCallback callback);
     readonly attribute boolean loading;
 
     void addEventListener(DOMString type,
                           EventListener listener,
                           optional boolean useCapture);
     void removeEventListener(DOMString type,
                              EventListener listener,
                              optional boolean useCapture);
     [RaisesException] boolean dispatchEvent(Event evt);
 };