Uses an open thread handle as the ThreadJoinId on Windows.

runtime/vm/os_thread_win.h

 // Copyright (c) 2012, 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_THREAD_WIN_H_
 #define VM_OS_THREAD_WIN_H_
 
 #if !defined(VM_OS_THREAD_H_)
 #error Do not include os_thread_win.h directly; use os_thread.h instead.
 #endif
 
 #include "platform/assert.h"
 #include "platform/globals.h"
 
 #include "vm/allocation.h"
 
 namespace dart {
 
 typedef DWORD ThreadLocalKey;
 typedef DWORD ThreadId;
-typedef DWORD ThreadJoinId;
+typedef HANDLE ThreadJoinId;
 
 
 static const ThreadLocalKey kUnsetThreadLocalKey = TLS_OUT_OF_INDEXES;
 
 
 class ThreadInlineImpl {
  private:
   ThreadInlineImpl() {}
   ~ThreadInlineImpl() {}
 
@@ skipping 135 matching lines @@
   static void InitOnce();
   static void Shutdown();
 
   friend class OS;
   friend class OSThread;
 };
 
 }  // namespace dart
 
 #endif  // VM_OS_THREAD_WIN_H_