Add UseCounters for non-standard MouseEvent IDL attributes

Source/core/events/MouseEvent.idl

 /*
  * Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 33 matching lines @@
                                        [Default=Undefined] optional long screenY,
                                        [Default=Undefined] optional long clientX,
                                        [Default=Undefined] optional long clientY,
                                        [Default=Undefined] optional boolean ctrlKey,
                                        [Default=Undefined] optional boolean altKey,
                                        [Default=Undefined] optional boolean shiftKey,
                                        [Default=Undefined] optional boolean metaKey,
                                        [Default=Undefined] optional unsigned short button,
                                        [Default=Undefined] optional EventTarget relatedTarget);
 
-    // extensions
-    readonly attribute long             offsetX;
-    readonly attribute long             offsetY;
-    readonly attribute long             x;
-    readonly attribute long             y;
-    readonly attribute Node             fromElement;
-    readonly attribute Node             toElement;
+    // Non-standard
+    [MeasureAs=MouseEventOffsetX] readonly attribute long offsetX;
+    [MeasureAs=MouseEventOffsetY] readonly attribute long offsetY;
+    [MeasureAs=MouseEventX] readonly attribute long x;
+    [MeasureAs=MouseEventY] readonly attribute long y;
+    [MeasureAs=MouseEventFromElement] readonly attribute Node fromElement;
+    [MeasureAs=MouseEventToElement] readonly attribute Node toElement;
 
-    readonly attribute DataTransfer     dataTransfer;
+    // FIXME: this belongs on the DragEvent interface
+    readonly attribute DataTransfer dataTransfer;
 };
-