VM: Small clean up and const-ness fix for Thread/OSThread constants.

runtime/vm/os_thread_win.cc

 // 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.
 
 #include "platform/globals.h"  // NOLINT
 #if defined(TARGET_OS_WINDOWS)
 
 #include "vm/growable_array.h"
 #include "vm/os_thread.h"
 
@@ skipping 68 matching lines @@
 #endif
     return errno;
   }
 
   // Close the handle, so we don't leak the thread object.
   CloseHandle(reinterpret_cast<HANDLE>(thread));
 
   return 0;
 }
 
-ThreadLocalKey OSThread::kUnsetThreadLocalKey = TLS_OUT_OF_INDEXES;
-ThreadId OSThread::kInvalidThreadId = 0;
-ThreadJoinId OSThread::kInvalidThreadJoinId = 0;
+
+const ThreadId OSThread::kInvalidThreadId = 0;
+const ThreadJoinId OSThread::kInvalidThreadJoinId = 0;
+
 
 ThreadLocalKey OSThread::CreateThreadLocal(ThreadDestructor destructor) {
   ThreadLocalKey key = TlsAlloc();
   if (key == kUnsetThreadLocalKey) {
     FATAL1("TlsAlloc failed %d", GetLastError());
   }
   ThreadLocalData::AddThreadLocal(key, destructor);
   return key;
 }
 
@@ skipping 596 matching lines @@
 #pragma data_seg(".CRT$XLB")
 PIMAGE_TLS_CALLBACK p_thread_callback_dart = OnDartThreadExit;
 
 // Reset the default section.
 #pragma data_seg()
 
 #endif  // _WIN64
 }  // extern "C"
 
 #endif  // defined(TARGET_OS_WINDOWS)