Implement for-in loop for proxies.

src/v8natives.js

 // Copyright 2011 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 919 matching lines @@
 }
 
 
 // For Harmony proxies
 function ToStringArray(obj, trap) {
   if (!IS_SPEC_OBJECT(obj)) {
     throw MakeTypeError("proxy_non_object_prop_names", [obj, trap]);
   }
   var n = ToUint32(obj.length);
   var array = new $Array(n);
-  var names = {}
+  var names = {}  // TODO(rossberg): use sets once they are ready.
   for (var index = 0; index < n; index++) {
     var s = ToString(obj[index]);
     if (s in names) {
       throw MakeTypeError("proxy_repeated_prop_name", [obj, trap, s])
     }
     array[index] = s;
-    names.s = 0;
+    names[s] = 0;
   }
   return array;
 }
 
 
 // ES5 section 15.2.3.4.
 function ObjectGetOwnPropertyNames(obj) {
   if (!IS_SPEC_OBJECT(obj))
     throw MakeTypeError("obj_ctor_property_non_object", ["getOwnPropertyNames"]);
 
@@ skipping 649 matching lines @@
 
 function SetUpFunction() {
   %CheckIsBootstrapping();
   InstallFunctions($Function.prototype, DONT_ENUM, $Array(
     "bind", FunctionBind,
     "toString", FunctionToString
   ));
 }
 
 SetUpFunction();