Make Date.prototype an ordinary object

test/mjsunit/date.js

Index: test/mjsunit/date.js
diff --git a/test/mjsunit/date.js b/test/mjsunit/date.js
index adebbd141f704cedd75e28b911084f87c8599060..33b5af4f00d85ad218b8321d36da6f243098fe62 100644
--- a/test/mjsunit/date.js
+++ b/test/mjsunit/date.js
@@ -341,6 +341,11 @@ date.getYear();
 assertThrows(function() { Date.prototype.getYear.call(""); }, TypeError);
 assertUnoptimized(Date.prototype.getYear);
 
+(function TestDatePrototypeOrdinaryObject() {
+  assertEquals(Object.prototype, Date.prototype.__proto__);
+  assertThrows(function () { Date.prototype.toString() }, TypeError);
+})();
+
 delete Date.prototype.getUTCFullYear;
 delete Date.prototype.getUTCMonth;
 delete Date.prototype.getUTCDate;