Remove leak of objects between isolated worlds on custom events.

Source/core/dom/CustomEvent.idl

Index: Source/core/dom/CustomEvent.idl
diff --git a/Source/core/dom/CustomEvent.idl b/Source/core/dom/CustomEvent.idl
index f4a67e4d21b82d2e69787247f0a2a74597278b65..5e9ecd0ab11b230b57918c79ec898235ac51d262 100644
--- a/Source/core/dom/CustomEvent.idl
+++ b/Source/core/dom/CustomEvent.idl
@@ -24,12 +24,12 @@
  */
 
 [
-    ConstructorTemplate=Event
+    CustomConstructor(DOMString type, optional CustomEventInit eventInitDict)
 ] interface CustomEvent : Event {
     [InitializedByEventConstructor, Custom] readonly attribute any detail;
 
-    void initCustomEvent([Default=Undefined] optional DOMString typeArg, 
-                         [Default=Undefined] optional boolean canBubbleArg, 
-                         [Default=Undefined] optional boolean cancelableArg, 
-                         [Default=Undefined] optional any detailArg);
+    [Custom] void initCustomEvent([Default=Undefined] optional DOMString typeArg,
+                                  [Default=Undefined] optional boolean canBubbleArg,
+                                  [Default=Undefined] optional boolean cancelableArg,
+                                  [Default=Undefined] optional any detailArg);
 };