Improve DST offset computation performance.

src/macros.py

 # Copyright 2006-2009 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 42 matching lines @@
 const kNewObjectTag = 1;
 
 # For date.js.
 const HoursPerDay      = 24;
 const MinutesPerHour   = 60;
 const SecondsPerMinute = 60;
 const msPerSecond      = 1000;
 const msPerMinute      = 60000;
 const msPerHour        = 3600000;
 const msPerDay         = 86400000;
+const msPerMonth       = 2592000000;
 
 # For apinatives.js
 const kUninitialized = -1;
 
 # Note: kDayZeroInJulianDay = ToJulianDay(1970, 0, 1).
 const kInvalidDate        = 'Invalid Date';
 const kDayZeroInJulianDay = 2440588;
 const kMonthMask          = 0x1e0;
 const kDayMask            = 0x01f;
 const kYearShift          = 9;
@@ skipping 40 matching lines @@
 # Last input and last subject are after the captures so we can omit them on
 # results returned from global searches.  Beware - these evaluate their
 # arguments twice.
 macro LAST_SUBJECT(array) = ((array)[1]);
 macro LAST_INPUT(array) = ((array)[2]);
 
 # REGEXP_FIRST_CAPTURE
 macro CAPTURE(index) = (3 + (index));
 const CAPTURE0 = 3;
 const CAPTURE1 = 4;