Revert of Make initEvent's first argument non-optional

third_party/WebKit/Source/core/events/Event.idl

Index: third_party/WebKit/Source/core/events/Event.idl
diff --git a/third_party/WebKit/Source/core/events/Event.idl b/third_party/WebKit/Source/core/events/Event.idl
index 518ce0ec0da58067521cf78a71533b8f76b960a7..4a9d2b027c62f7e9620289f96edf8449857a564d 100644
--- a/third_party/WebKit/Source/core/events/Event.idl
+++ b/third_party/WebKit/Source/core/events/Event.idl
@@ -49,7 +49,10 @@
 
     [CallWith=ScriptState] readonly attribute DOMHighResTimeStamp timeStamp;
 
-    [Measure] void initEvent(DOMString type, optional boolean bubbles = false, optional boolean cancelable = false);
+    // FIXME: initEvent()'s arguments should not be optional.
+    [Measure] void initEvent([Default=Undefined] optional DOMString type,
+                             [Default=Undefined] optional boolean bubbles,
+                             [Default=Undefined] optional boolean cancelable);
 
     // Non-standard APIs
     [MeasureAs=EventSrcElement] readonly attribute EventTarget srcElement;