document.lastModified should consider user's local time zone

Source/wtf/DateMath.cpp

 /*
  * 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) 2007-2009 Torch Mobile, Inc.
  * Copyright (C) 2010 &yet, LLC. (nate@andyet.net)
  *
  * The Original Code is Mozilla Communicator client code, released
  * March 31, 1998.
  *
@@ skipping 340 matching lines @@
         return year;
 
     int quotient = difference / 28;
     int product = (quotient) * 28;
 
     year += product;
     ASSERT((year >= minYear && year <= maxYear) || (product - year == static_cast<int>(std::numeric_limits<double>::quiet_NaN())));
     return year;
 }
 
-int32_t calculateUTCOffset()
+static int32_t calculateUTCOffset()
 {
 #if OS(WIN)
     TIME_ZONE_INFORMATION timeZoneInformation;
     GetTimeZoneInformation(&timeZoneInformation);
     int32_t bias = timeZoneInformation.Bias + timeZoneInformation.StandardBias;
     return -bias * 60 * 1000;
 #else
     time_t localTime = time(0);
     tm localt;
     getLocalTime(&localTime, &localt);
@@ skipping 52 matching lines @@
 
     double diff = ((localTM.tm_hour - offsetHour) * secondsPerHour) + ((localTM.tm_min - offsetMinute) * 60);
 
     if (diff < 0)
         diff += secondsPerDay;
 
     return (diff * msPerSecond);
 }
 
 // Get the DST offset, given a time in UTC
-double calculateDSTOffset(double ms, double utcOffset)
+static double calculateDSTOffset(double ms, double utcOffset)
 {
     // On Mac OS X, the call to localtime (see calculateDSTOffsetSimple) will return historically accurate
     // DST information (e.g. New Zealand did not have DST from 1946 to 1974) however the JavaScript
     // standard explicitly dictates that historical information should not be considered when
     // determining DST. For this reason we shift away from years that localtime can handle but would
     // return historically accurate information.
     int year = msToYear(ms);
     int equivalentYear = equivalentYearForDST(year);
     if (year != equivalentYear) {
         bool leapYear = isLeapYear(year);
@@ skipping 429 matching lines @@
     stringBuilder.append(' ');
 
     stringBuilder.append(utcOffset > 0 ? '+' : '-');
     int absoluteUTCOffset = abs(utcOffset);
     stringBuilder.append(twoDigitStringFromNumber(absoluteUTCOffset / 60));
     stringBuilder.append(twoDigitStringFromNumber(absoluteUTCOffset % 60));
 
     return stringBuilder.toString();
 }
 
+double convertToLocalTime(double ms)
+{
+    double utcOffset = calculateUTCOffset();
+    double dstOffset = calculateDSTOffset(ms, utcOffset);
+    return (ms + utcOffset + dstOffset);
+}
+
 } // namespace WTF