Fix stack trace accessor behavior.

test/mjsunit/stack-traces.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 313 matching lines @@
   message = e.message;
 }
 
 assertEquals("abc", message);
 
 // Test that modifying Error.prepareStackTrace by itself works.
 Error.prepareStackTrace = function() { Error.prepareStackTrace = "custom"; };
 new Error().stack;
 
 assertEquals("custom", Error.prepareStackTrace);
+
+// Check that the formatted stack trace can be set to undefined.
+error = new Error();
+error.stack = undefined;
+assertEquals(undefined, error.stack);
+
+// Check that the stack trace accessors are not forcibly set.
+var my_error = {};
+Object.freeze(my_error);
+assertThrows(function() { Error.captureStackTrace(my_error); });