Fix JSON.stringify wrt harmony proxies.

src/json.js

 // Copyright 2009 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 197 matching lines @@
 
 
 function SetUpJSON() {
   %CheckIsBootstrapping();
   InstallFunctions($JSON, DONT_ENUM, $Array(
     "parse", JSONParse,
     "stringify", JSONStringify
   ));
 }
 
+
+function JSONSerializeAdapter(key, object) {
+  var holder = {};
+  holder[key] = object;
+  // No need to pass the actual holder since there is no replacer function.
+  return JSONSerialize(key, holder, void 0, new InternalArray(), "", "");
+}
+
 SetUpJSON();