Reapply the non-MathExtras parts of

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 777 matching lines @@
     bool haveTZ;
     int offset;
     double ms = parseDateFromNullTerminatedCharacters(dateString, haveTZ, offset);
     if (std::isnan(ms))
         return std::numeric_limits<double>::quiet_NaN();
 
     // fall back to local timezone
     if (!haveTZ) {
         double utcOffset = calculateUTCOffset();
         double dstOffset = calculateDSTOffset(ms, utcOffset);
-        offset = (utcOffset + dstOffset) / msPerMinute;
+        offset = static_cast<int>((utcOffset + dstOffset) / msPerMinute);
     }
     return ms - (offset * msPerMinute);
 }
 
 // See http://tools.ietf.org/html/rfc2822#section-3.3 for more information.
 String makeRFC2822DateString(unsigned dayOfWeek, unsigned day, unsigned month, unsigned year, unsigned hours, unsigned minutes, unsigned seconds, int utcOffset)
 {
     StringBuilder stringBuilder;
     stringBuilder.append(weekdayName[dayOfWeek]);
     stringBuilder.appendLiteral(", ");
@@ skipping 20 matching lines @@
 }
 
 double convertToLocalTime(double ms)
 {
     double utcOffset = calculateUTCOffset();
     double dstOffset = calculateDSTOffset(ms, utcOffset);
     return (ms + utcOffset + dstOffset);
 }
 
 } // namespace WTF