Add UseCounter for initMessageEvent (including prefixed version.)

Source/core/events/MessageEvent.idl

 /*
  * Copyright (C) 2007 Henry Mason <hmason@mac.com>
  * Copyright (C) 2011 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 17 matching lines @@
 [
     EventConstructor,
     GlobalContext=Window&WorkerGlobalScope,
     RaisesException=Constructor,
 ] interface MessageEvent : Event {
     [InitializedByEventConstructor] readonly attribute DOMString origin;
     [InitializedByEventConstructor] readonly attribute DOMString lastEventId;
     [InitializedByEventConstructor] readonly attribute EventTarget? source; // May be a Window or a MessagePort
     [InitializedByEventConstructor, Custom=Getter] readonly attribute any data;
     [InitializedByEventConstructor] readonly attribute MessagePort[] ports;
-    [Custom] void initMessageEvent([Default=Undefined] optional DOMString typeArg,
+    [Custom, MeasureAs=InitMessageEvent] void initMessageEvent([Default=Undefined] optional DOMString typeArg,
                                    [Default=Undefined] optional boolean canBubbleArg,
                                    [Default=Undefined] optional boolean cancelableArg,
                                    [Default=Undefined] optional any dataArg,
                                    [Default=Undefined] optional DOMString originArg,
                                    [Default=Undefined] optional DOMString lastEventIdArg,
                                    [Default=Undefined] optional Window sourceArg,
                                    [Default=Undefined] optional Array messagePorts);
 
-    [Custom] void webkitInitMessageEvent([Default=Undefined] optional DOMString typeArg,
+    [Custom, MeasureAs=PrefixedInitMessageEvent] void webkitInitMessageEvent([Default=Undefined] optional DOMString typeArg,
                                          [Default=Undefined] optional boolean canBubbleArg,
                                          [Default=Undefined] optional boolean cancelableArg,
                                          [Default=Undefined] optional any dataArg,
                                          [Default=Undefined] optional DOMString originArg,
                                          [Default=Undefined] optional DOMString lastEventIdArg,
                                          [Default=Undefined] optional Window sourceArg,
                                          [Default=Undefined] optional Array transferables);
 };