Date() should not depend on Date.prototype.toString

test/mjsunit/date.js

 // Copyright 2008 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 331 matching lines @@
 assertUnoptimized(Date.prototype.getYear);
 
 delete Date.prototype.getUTCFullYear;
 delete Date.prototype.getUTCMonth;
 delete Date.prototype.getUTCDate;
 delete Date.prototype.getUTCHours;
 delete Date.prototype.getUTCMinutes;
 delete Date.prototype.getUTCSeconds;
 delete Date.prototype.getUTCMilliseconds;
 date.toISOString();
+
+(function TestDeleteToString() {
+  assertTrue(delete Date.prototype.toString);
+  assertTrue('[object Date]' !== Date());
+})();