Add fast path for FastProperty objects in JSON.stringify.

test/mjsunit/json2.js

 // Copyright 2012 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 115 matching lines @@
 delete fast_double[2];
 assertTrue(%HasFastDoubleElements(fast_double));
 assertEquals("[1.1,2,7,4]", JSON.stringify(fast_double));
 
 var fast_obj = [1, 2, {}, {}];
 fast_obj.__proto__ = [7, 7, 7, 7];
 
 delete fast_obj[2];
 assertTrue(%HasFastObjectElements(fast_obj));
 assertEquals("[1,2,7,{}]", JSON.stringify(fast_obj));
+
+var getter_side_effect = { a: 1,
+                           get b() {
+                             delete this.a;
+                             delete this.c;
+                             this.e = 5;
+                             return 2;
+                           },
+                           c: 3,
+                           d: 4 };
+assertEquals('{"a":1,"b":2,"d":4}', JSON.stringify(getter_side_effect));
+assertEquals('{"b":2,"d":4,"e":5}', JSON.stringify(getter_side_effect));
+
+var non_enum = {};
+non_enum.a = 1;
+Object.defineProperty(non_enum, "b", { value: 2, enumerable: false });
+non_enum.c = 3;
+assertEquals('{"a":1,"c":3}', JSON.stringify(non_enum));