IDL: Support optional argument default value syntax

Source/core/timing/Performance.idl

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 21 matching lines @@
 // See: http://www.w3.org/TR/navigation-timing/
 [
     WillBeGarbageCollected
 ] interface Performance : EventTarget {
     readonly attribute PerformanceNavigation navigation;
     readonly attribute PerformanceTiming timing;
     readonly attribute MemoryInfo memory;
 
     [MeasureAs=UnprefixedPerformanceTimeline] sequence<PerformanceEntry> getEntries();
     [MeasureAs=UnprefixedPerformanceTimeline] sequence<PerformanceEntry> getEntriesByType(DOMString entryType);
-    [MeasureAs=UnprefixedPerformanceTimeline] sequence<PerformanceEntry> getEntriesByName(DOMString name, [Default=NullString] optional DOMString entryType);
+    [MeasureAs=UnprefixedPerformanceTimeline] sequence<PerformanceEntry> getEntriesByName(DOMString name, optional DOMString entryType = null);
 
     [MeasureAs=PrefixedPerformanceClearResourceTimings] void webkitClearResourceTimings();
     [MeasureAs=PrefixedPerformanceSetResourceTimingBufferSize] void webkitSetResourceTimingBufferSize(unsigned long maxSize);
 
     attribute EventHandler onwebkitresourcetimingbufferfull;
 
     // See http://www.w3.org/TR/2012/CR-user-timing-20120726/
     [RaisesException,MeasureAs=UnprefixedUserTiming] void mark(DOMString markName);
-    [MeasureAs=UnprefixedUserTiming] void clearMarks([Default=NullString] optional  DOMString markName);
+    [MeasureAs=UnprefixedUserTiming] void clearMarks(optional DOMString markName = null);
 
-    [RaisesException,MeasureAs=UnprefixedUserTiming] void measure(DOMString measureName, [Default=NullString] optional DOMString startMark, [Default=NullString] optional DOMString endMark);
-    [MeasureAs=UnprefixedUserTiming] void clearMeasures([Default=NullString] optional DOMString measureName);
+    [RaisesException,MeasureAs=UnprefixedUserTiming] void measure(DOMString measureName, optional DOMString startMark = null, optional DOMString endMark = null);
+    [MeasureAs=UnprefixedUserTiming] void clearMeasures(optional DOMString measureName = null);
 
     // See http://www.w3.org/TR/hr-time/ for details.
     double now();
 };