Avoid some unnecessary fast-properties map creations.

test/mjsunit/regress/regress-crbug-137689.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 26 matching lines @@
 Object.defineProperty(o, "foo", { get: getter, configurable: true });
 Object.defineProperty(o2, "foo", { get: getter, configurable: true });
 assertTrue(%HaveSameMap(o, o2));
 
 Object.defineProperty(o, "bar", { get: getter2 });
 Object.defineProperty(o2, "bar", { get: getter2 });
 assertTrue(%HaveSameMap(o, o2));
 
 Object.defineProperty(o, "foo", { set: setter, configurable: true });
 Object.defineProperty(o2, "foo", { set: setter, configurable: true });
-// TODO(ishell): this should eventually become assertTrue().
-assertFalse(%HaveSameMap(o, o2));
+assertTrue(%HaveSameMap(o, o2));