Reapply "Add support for timezone offset and timezone name."

runtime/vm/os.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_OS_H_
 #define VM_OS_H_
 
 #include "vm/globals.h"
 
 // Forward declarations.
@@ skipping 24 matching lines @@
   // The given year is offset by 1900. The given month is 0-based.
   // Returns true if the conversion succeeds, false otherwise.
   static bool MkGmTime(tm* tm, int64_t* seconds_result);
 
   // Takes the broken down date and time in local timezone and computes the
   // seconds since epoch (midnight, January 1, 1970 UTC).
   // The given year is offset by 1900. The given month is 0-based.
   // Returns true if the conversion succeeds, false otherwise.
   static bool MkTime(tm* tm, int64_t* seconds_result);
 
+  // Returns the abbreviated time-zone name for the given instant.
+  // For example "CET" or "CEST".
+  static bool GetTimeZoneName(int64_t seconds_since_epoch,
+                              const char** name_result);
+
+  // Returns the difference in seconds between local time and UTC for the given
+  // instant.
+  // For example 3600 for CET, and 7200 for CEST.
+  static bool GetTimeZoneOffsetInSeconds(int64_t seconds_since_epoch,
+                                         int* offset_result);
+
   // Returns the current time in milliseconds measured
   // from midnight January 1, 1970 UTC.
   static int64_t GetCurrentTimeMillis();
 
   // Returns the current time in microseconds measured
   // from midnight January 1, 1970 UTC.
   static int64_t GetCurrentTimeMicros();
 
   // Returns the activation frame alignment constraint or zero if
   // the platform doesn't care. Guaranteed to be a power of two.
@@ skipping 42 matching lines @@
   static void Shutdown();
 
   static void Abort();
 
   static void Exit(int code);
 };
 
 }  // namespace dart
 
 #endif  // VM_OS_H_