document.lastModified should consider user's local time zone

Source/wtf/DateMath.h

 /*
  * Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
  * Copyright (C) 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2010 Research In Motion Limited. All rights reserved.
  *
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  *
  * The contents of this file are subject to the Mozilla Public License Version
  * 1.1 (the "License"); you may not use this file except in compliance with
@@ skipping 60 matching lines @@
 WTF_EXPORT bool isLeapYear(int year);
 
 // Returns the number of days from 1970-01-01 to the specified date.
 WTF_EXPORT double dateToDaysFrom1970(int year, int month, int day);
 WTF_EXPORT int msToYear(double ms);
 WTF_EXPORT int dayInYear(int year, int month, int day);
 WTF_EXPORT int dayInYear(double ms, int year);
 WTF_EXPORT int monthFromDayInYear(int dayInYear, bool leapYear);
 WTF_EXPORT int dayInMonthFromDayInYear(int dayInYear, bool leapYear);
 
-// Returns offset milliseconds for UTC and DST.
-WTF_EXPORT int32_t calculateUTCOffset();
-WTF_EXPORT double calculateDSTOffset(double ms, double utcOffset);
+// Returns milliseconds with UTC and DST.
+WTF_EXPORT double convertToLocalTime(double ms);
 
 } // namespace WTF
 
 using WTF::isLeapYear;
 using WTF::dateToDaysFrom1970;
 using WTF::dayInMonthFromDayInYear;
 using WTF::dayInYear;
 using WTF::minutesPerHour;
 using WTF::monthFromDayInYear;
 using WTF::msPerDay;
 using WTF::msPerHour;
 using WTF::msPerMinute;
 using WTF::msPerSecond;
 using WTF::msToYear;
 using WTF::secondsPerMinute;
 using WTF::parseDateFromNullTerminatedCharacters;
 using WTF::makeRFC2822DateString;
-using WTF::calculateUTCOffset;
-using WTF::calculateDSTOffset;
+using WTF::convertToLocalTime;
 
 #endif // DateMath_h