Fix Windows time zone name extraction. Update API docs

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.
 struct tm;
 
 namespace dart {
 
 // Forward declarations.
 class Isolate;
 class Zone;
 
 // Interface to the underlying OS platform.
 class OS {
  public:
   // Returns the name of the given OS. For example "linux".
   static const char* Name();
 
   // Returns the current process id.
   static intptr_t ProcessId();
 
-  // Returns the abbreviated time-zone name for the given instant.
-  // For example "CET" or "CEST".
+  // Returns a time-zone name for the given instant.
+  // The name is provided by the underlying platform.
+  // The returned string may be Zone allocated.
   static const char* GetTimeZoneName(int64_t seconds_since_epoch);
 
   // Returns the difference in seconds between local time and UTC for the given
   // instant.
   // For example 3600 for CET, and 7200 for CEST.
   static int GetTimeZoneOffsetInSeconds(int64_t seconds_since_epoch);
 
   // Returns the difference in seconds between local time and UTC when no
   // daylight saving is active.
   // For example 3600 in CET and CEST.
@@ skipping 123 matching lines @@
   static void Shutdown();
 
   static void Abort();
 
   static void Exit(int code);
 };
 
 }  // namespace dart
 
 #endif  // VM_OS_H_