Set the TZ env to get the UTC-ms since epoch.

runtime/vm/os_win.cc

Index: runtime/vm/os_win.cc
diff --git a/runtime/vm/os_win.cc b/runtime/vm/os_win.cc
index 71020dec96b14829abc72b2f2b793f6df771cbdd..ec93c8211d274e1fbc81b944e76deaa5fe8a3af4 100644
--- a/runtime/vm/os_win.cc
+++ b/runtime/vm/os_win.cc
@@ -10,63 +10,46 @@
 
 namespace dart {
 
-bool OS::BreakDownSecondsSinceEpoch(time_t seconds_since_epoch,
-                                    bool in_utc,
-                                    BrokenDownDate* result) {
-  struct tm tm_result;
-  errno_t error_code;
-  if (in_utc) {
-    error_code = gmtime_s(&tm_result, &seconds_since_epoch);
-  } else {
-    // TODO(floitsch): we should be able to call tzset only once during
-    // initialization.
-    tzset();  // Make sure the libc knows about the local zone.
-    error_code = localtime_s(&tm_result, &seconds_since_epoch);
-  }
-  result->year = tm_result.tm_year;
-  result->month= tm_result.tm_mon;
-  result->day = tm_result.tm_mday;
-  result->hours = tm_result.tm_hour;
-  result->minutes = tm_result.tm_min;
-  result->seconds = tm_result.tm_sec;
+bool OS::GmTime(int64_t seconds_since_epoch, tm* tm_result) {
+  time_t seconds = static_cast<time_t>(seconds_since_epoch);
+  if (seconds != seconds_since_epoch) return false;
+  errno_t error_code = gmtime_s(tm_result, &seconds);
+  return error_code == 0;
+}
+
+
+bool OS::LocalTime(int64_t seconds_since_epoch, tm* tm_result) {
+  time_t seconds = static_cast<time_t>(seconds_since_epoch);
+  if (seconds != seconds_since_epoch) return false;
+  errno_t error_code = localtime_s(tm_result, &seconds);
   return error_code == 0;
 }
 
 
-bool OS::BrokenDownToSecondsSinceEpoch(
-    const BrokenDownDate& broken_down, bool in_utc, time_t* result) {
-  struct tm tm_broken_down;
-  // mktime takes the years since 1900.
-  tm_broken_down.tm_year = broken_down.year;
-  tm_broken_down.tm_mon = broken_down.month;
-  tm_broken_down.tm_mday = broken_down.day;
-  tm_broken_down.tm_hour = broken_down.hours;
-  tm_broken_down.tm_min = broken_down.minutes;
-  tm_broken_down.tm_sec = broken_down.seconds;
+bool OS::MkGmTime(tm* tm, int64_t* seconds_result) {
+  // Disable daylight saving.
+  tm->tm_isdst = 0;
   // Set wday to an impossible day, so that we can catch bad input.
-  tm_broken_down.tm_wday = -1;
-  // Make sure the libc knows about the local zone.
-  // In case of 'in_utc' this call is mainly for multi-threading issues. If
-  // another thread uses a time-function it will set the timezone. The timezone
-  // adjustement below would then not work anymore.
-  // TODO(floitsch): we should be able to call tzset only once during
-  // initialization.
-  tzset();
-  if (in_utc) {
-    // Disable daylight saving in utc mode.
-    tm_broken_down.tm_isdst = 0;
-    // mktime assumes that the given date is local time zone.
-    *result = mktime(&tm_broken_down);
-    // Remove the timezone.
-    *result -= timezone;
-  } else {
-    // Let libc figure out if daylight saving is active.
-    tm_broken_down.tm_isdst = -1;
-    *result = mktime(&tm_broken_down);
+  tm->tm_wday = -1;
+  time_t seconds = _mkgmtime(tm);
+  if ((seconds == -1) && (tm->tm_wday == -1)) {
+    return false;
   }
-  if ((*result == -1) && (tm_broken_down.tm_wday == -1)) {
+  *seconds_result = seconds;
+  return true;
+}
+
+
+bool OS::MkTime(tm* tm, int64_t* seconds_result) {
+  // Let the libc figure out if daylight saving is active.
+  tm->tm_isdst = -1;
+  // Set wday to an impossible day, so that we can catch bad input.
+  tm->tm_wday = -1;
+  time_t seconds = mktime(tm);
+  if ((seconds == -1) && (tm->tm_wday == -1)) {
     return false;
   }
+  *seconds_result = seconds;
   return true;
 }