Avoid some unnecessary fast-properties map creations.

test/mjsunit/object-freeze.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 285 matching lines @@
 accessorDidRun = false;
 obj.accessor = 'ignored value';
 assertTrue(accessorDidRun);
 
 // Test for regression in mixed accessor/data property objects.
 // The strict function is one such object.
 assertTrue(Object.isFrozen(Object.freeze(function(){"use strict";})));
 
 // Also test a simpler case
 obj = {};
-Object.defineProperty(obj, 'accessor', {
+Object.defineProperty(obj, 'accessor2', {
   get: function() { return 42 },
   set: function() { accessorDidRun = true },
   configurable: true,
   enumerable: true
 });
 obj.data = 'foo';
 assertTrue(%HasFastProperties(obj));
 Object.freeze(obj);
 assertTrue(%HasFastProperties(obj));
 assertTrue(Object.isFrozen(obj));
@@ skipping 15 matching lines @@
 assertThrows(function() { obj.splice(0,1,1); }, TypeError);
 assertTrue(Object.isFrozen(obj));
 
 // Verify that unshift() with no arguments will fail if it reifies from
 // the prototype into the object.
 obj = [1,,3];
 obj.__proto__[1] = 1;
 assertEquals(1, obj[1]);
 Object.freeze(obj);
 assertThrows(function() { obj.unshift(); }, TypeError);