Fix the return type of the date set methods.

src/date.js

 // Copyright 2006-2008 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 498 matching lines @@
   return UTC_DATE_VALUE(this);
 }
 
 
 // ECMA 262 - 15.9.5.28
 function DateSetMilliseconds(ms) {
   CHECK_DATE(this);
   var t = LOCAL_DATE_VALUE(this);
   ms = ToNumber(ms);
   var time = MakeTime(LOCAL_HOUR(this), LOCAL_MIN(this), LOCAL_SEC(this), ms);
-  SET_LOCAL_DATE_VALUE(this, MakeDate(LOCAL_DAYS(this), time));
-  return this;
+  return SET_LOCAL_DATE_VALUE(this, MakeDate(LOCAL_DAYS(this), time));
 }
 
 
 // ECMA 262 - 15.9.5.29
 function DateSetUTCMilliseconds(ms) {
   CHECK_DATE(this);
   var t = UTC_DATE_VALUE(this);
   ms = ToNumber(ms);
   var time = MakeTime(UTC_HOUR(this),
                       UTC_MIN(this),
@@ skipping 334 matching lines @@
     "toGMTString", DateToGMTString,
     "toUTCString", DateToUTCString,
     "getYear", DateGetYear,
     "setYear", DateSetYear,
     "toISOString", DateToISOString,
     "toJSON", DateToJSON
   ));
 }
 
 SetUpDate();