Add remaining @@toStringTag symbols to builtins

test/mjsunit/es6/json.js

Index: test/mjsunit/es6/json.js
diff --git a/test/mjsunit/es6/json.js b/test/mjsunit/es6/json.js
new file mode 100644
index 0000000000000000000000000000000000000000..3fad08318fa86a58de2804076af12761ff8c49a1
--- /dev/null
+++ b/test/mjsunit/es6/json.js
@@ -0,0 +1,15 @@
+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-tostring
+
+function testJSONToString() {
+  assertEquals('[object JSON]', "" + JSON);
+  assertEquals("JSON", JSON[Symbol.toStringTag]);
+  var desc = Object.getOwnPropertyDescriptor(JSON, Symbol.toStringTag);
+  assertTrue(desc.configurable);
+  assertFalse(desc.writable);
+  assertEquals("JSON", desc.value);
+}
+testJSONToString();