Support intriscDefaultProto for Error functions

test/mjsunit/error-constructors.js

 // Copyright 2011 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 110 matching lines @@
               SyntaxError, ReferenceError, TypeError, MyError];
 for (var i in errors) {
   errors[i].prototype.__defineGetter__("name", function() { return "my"; });
   errors[i].prototype.__defineGetter__("message", function() { return "moo"; });
   var e = new errors[i];
   assertEquals("my: moo", e.toString());
 }
 
 
 Error.prototype.toString = Object.prototype.toString;
-assertEquals("[object Error]", Error.prototype.toString());
+assertEquals("[object Object]", Error.prototype.toString());
 assertEquals(Object.prototype, Error.prototype.__proto__);
 var e = new Error("foo");
 assertEquals("[object Error]", e.toString());