Add UseCounters for init*Event methods that aren't already measured

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 86aad716be09bf0dd42ccf8e3c2d79101a0e2495..4d4cb085c639989686d3f31d2cb996645c8f84df 100644
--- a/Source/core/events/CustomEvent.idl
+++ b/Source/core/events/CustomEvent.idl
@@ -32,8 +32,8 @@
     [Custom=Getter] readonly attribute any detail;
 
     // FIXME: initCustomEvent()'s arguments should not be optional.
-    [Custom] void initCustomEvent([Default=Undefined] optional DOMString typeArg,
-                                  [Default=Undefined] optional boolean canBubbleArg,
-                                  [Default=Undefined] optional boolean cancelableArg,
-                                  [Default=Undefined] optional any detailArg);
+    [Custom, Measure] void initCustomEvent([Default=Undefined] optional DOMString type,
+                                           [Default=Undefined] optional boolean bubbles,
+                                           [Default=Undefined] optional boolean cancelable,
+                                           [Default=Undefined] optional any detail);
 };