Object.getOwnPropertyNames should be free of duplicates

src/v8natives.js

 // Copyright 2006-2008 the V8 project authors. 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.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 659 matching lines @@
   // Get names for named interceptor properties if any.
 
   if (%GetInterceptorInfo(obj) & 2) {
     var namedInterceptorNames =
         %GetNamedInterceptorPropertyNames(obj);
     if (namedInterceptorNames) {
       propertyNames = propertyNames.concat(namedInterceptorNames);
     }
   }
 
-  // Property names are expected to be strings.
-  for (var i = 0; i < propertyNames.length; ++i)
-    propertyNames[i] = ToString(propertyNames[i]);
+  // Property names are expected to be unique strings.
+  var propertySet = {};
+  var j = 0;
+  for (var i = 0; i < propertyNames.length; ++i) {
+    var name = ToString(propertyNames[i]);
+    if (name in propertySet)
+      continue;
+    propertySet[name] = true;
+    propertyNames[j++] = name;
+  }
+  propertyNames.length = j;
 
   return propertyNames;
 }
 
 
 // ES5 section 15.2.3.5.
 function ObjectCreate(proto, properties) {
   if (!IS_SPEC_OBJECT_OR_NULL(proto)) {
     throw MakeTypeError("proto_object_or_null", [proto]);
   }
@@ skipping 337 matching lines @@
 
 // ----------------------------------------------------------------------------
 
 function SetupFunction() {
   InstallFunctions($Function.prototype, DONT_ENUM, $Array(
     "toString", FunctionToString
   ));
 }
 
 SetupFunction();