Add UseCounters for non-standard UIEvent IDL attributes

Source/core/events/UIEvent.idl

Index: Source/core/events/UIEvent.idl
diff --git a/Source/core/events/UIEvent.idl b/Source/core/events/UIEvent.idl
index df8ec347ddcd25615ea8415f8818619925a32ec1..4d025d8050b968d75e006eb29804a3a86692fd14 100644
--- a/Source/core/events/UIEvent.idl
+++ b/Source/core/events/UIEvent.idl
@@ -29,13 +29,14 @@
                                     [Default=Undefined] optional Window view,
                                     [Default=Undefined] optional long detail);
 
-    // extensions
-    readonly attribute long                 keyCode;
-    readonly attribute long                 charCode;
-    readonly attribute long                 layerX;
-    readonly attribute long                 layerY;
-    readonly attribute long                 pageX;
-    readonly attribute long                 pageY;
-    readonly attribute long                 which;
-};
+    // Non-standard
+    [MeasureAs=UIEventLayerX] readonly attribute long layerX;
+    [MeasureAs=UIEventLayerY] readonly attribute long layerY;
+    [MeasureAs=UIEventPageX] readonly attribute long pageX;
+    [MeasureAs=UIEventPageY] readonly attribute long pageY;
 
+    // FIXME: these belong on the KeyboardEvent interface
+    readonly attribute long keyCode;
+    readonly attribute long charCode;
+    readonly attribute long which;
+};