After assignment return right hand side value instead of undefined

test/mjsunit/object-prevent-extensions.js

 // Copyright 2010 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 96 matching lines @@
 
 // Test that attributes on functions are also handled correctly.
 function foo() {
   return 42;
 }
 
 Object.preventExtensions(foo);
 
 foo.x = 29;
 assertEquals(undefined, foo.x);
+
+// when Object.isExtensible(o) === false
+// assignment should return right hand side value
+var o = Object.preventExtensions({});
+var v = o.v = 50;
+assertEquals(undefined, o.v);
+assertEquals(50, v);
+
+// test same behavior as above, but for integer properties
+var n = o[0] = 100;
+assertEquals(undefined, o[0]);
+assertEquals(100, n);