Handle edge cases in basic JSON.stringify.

test/mjsunit/regress/regress-json-stringify-gc.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 19 matching lines @@
 for (var i = 0; i < 128; i++) {
   new_space_string += String.fromCharCode((Math.random() * 26 + 65) | 0);
 }
 for (var i = 0; i < 10000; i++) a.push(new_space_string);
 
 // At some point during the first stringify, allocation causes a GC and
 // new_space_string is moved to old space. Make sure that this does not
 // screw up reading from the correct location.
 json1 = JSON.stringify(a);
 json2 = JSON.stringify(a);
-assertEquals(json1, json2);
+assertEquals(json1, json2, "GC caused JSON.stringify to fail.");