[bindings] Make all CustomEvent.initCustomEvent arguments non-optional and remove custom binding.

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 4d4cb085c639989686d3f31d2cb996645c8f84df..5e6d7abd36049c1f94cae0be83e1847462b91137 100644
--- a/Source/core/events/CustomEvent.idl
+++ b/Source/core/events/CustomEvent.idl
@@ -31,9 +31,5 @@
 ] interface CustomEvent : Event {
     [Custom=Getter] readonly attribute any detail;
 
-    // FIXME: initCustomEvent()'s arguments should not be optional.
-    [Custom, Measure] void initCustomEvent([Default=Undefined] optional DOMString type,
-                                           [Default=Undefined] optional boolean bubbles,
-                                           [Default=Undefined] optional boolean cancelable,
-                                           [Default=Undefined] optional any detail);
+    [Measure] void initCustomEvent(DOMString type, boolean bubbles, boolean cancelable, any detail);
 };