IDL: Add any support to IDL dictionary and use it in CustomEventInit

Source/core/events/CustomEvent.idl

Index: Source/core/events/CustomEvent.idl
diff --git a/Source/core/events/CustomEvent.idl b/Source/core/events/CustomEvent.idl
index 072cc26af4daf282b635816078fdf9479d32219f..86aad716be09bf0dd42ccf8e3c2d79101a0e2495 100644
--- a/Source/core/events/CustomEvent.idl
+++ b/Source/core/events/CustomEvent.idl
@@ -26,10 +26,10 @@
 // https://dom.spec.whatwg.org/#interface-customevent
 
 [
-    EventConstructor,
-    Exposed=(Window,Worker)
+    Constructor(DOMString type, optional CustomEventInit eventInitDict),
+    Exposed=(Window,Worker),
 ] interface CustomEvent : Event {
-    [Custom=Getter, InitializedByEventConstructor] readonly attribute any detail;
+    [Custom=Getter] readonly attribute any detail;
 
     // FIXME: initCustomEvent()'s arguments should not be optional.
     [Custom] void initCustomEvent([Default=Undefined] optional DOMString typeArg,