Speed up creation of Objects whose prototype has dictionary elements

test/mjsunit/fast-prototype.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 96 matching lines @@
 assertTrue(%HasFastProperties(x));
 for (key in x) {
   assertTrue(key == 'a');
   break;
 }
 delete x.b;
 for (key in x) {
   assertTrue(key == 'a');
   break;
 }
-assertFalse(%HasFastProperties(x));
+assertTrue(%HasFastProperties(x));
 x.d = 4;
-assertFalse(%HasFastProperties(x));
+assertTrue(%HasFastProperties(x));
 for (key in x) {
   assertTrue(key == 'a');
   break;
 }