Error.captureStackTrace should define "stack" property as configurable.

test/mjsunit/regress/regress-crbug-393988.js

Index: test/mjsunit/regress/regress-crbug-393988.js
diff --git a/test/mjsunit/harmony/regress/regress-3426.js b/test/mjsunit/regress/regress-crbug-393988.js
similarity index 59%
copy from test/mjsunit/harmony/regress/regress-3426.js
copy to test/mjsunit/regress/regress-crbug-393988.js
index c3b11a1792f8c8adaf05788d9604a2c9c9f5dcde..9543e1e4c4aaed07c9a5743500f004ca3c677a10 100644
--- a/test/mjsunit/harmony/regress/regress-3426.js
+++ b/test/mjsunit/regress/regress-crbug-393988.js
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --harmony-scoping
-
-assertThrows("(function() { 'use strict'; { let f; var f; } })", SyntaxError);
+var o = {};
+Error.captureStackTrace(o);
+Object.defineProperty(o, "stack", { value: 1 });
+assertEquals(1, o.stack);