Fix invalid attributes when generalizing because of incompatible map change.

test/mjsunit/regress/regress-crbug-382143.js

Index: test/mjsunit/regress/regress-crbug-382143.js
diff --git a/test/mjsunit/regress/regress-crbug-382143.js b/test/mjsunit/regress/regress-crbug-382143.js
new file mode 100644
index 0000000000000000000000000000000000000000..9f37b2e478c5f647bd02cb94a009c1c1453b083e
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-382143.js
@@ -0,0 +1,16 @@
+// Copyright 2013 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.
+
+function A() {
+  Object.defineProperty(this, "x", { set: function () {}, get: function () {}});
+  this.a = function () { return 1; }
+}
+
+function B() {
+  A.apply( this );
+  this.a = function () { return 2; }
+}
+
+var b = new B();
+assertTrue(Object.getOwnPropertyDescriptor(b, "a").enumerable);