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

runtime/vm/os_thread.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_H_
 #define VM_OS_THREAD_H_
 
 #include "platform/globals.h"
 #include "vm/allocation.h"
 #include "vm/globals.h"
@@ skipping 157 matching lines @@
   static bool Compare(ThreadId a, ThreadId b);
   static void GetThreadCpuUsage(ThreadId thread_id, int64_t* cpu_usage);
 
   // Called at VM startup and shutdown.
   static void InitOnce();
 
   static bool IsThreadInList(ThreadId join_id);
 
   static const intptr_t kStackSizeBuffer = (4 * KB * kWordSize);
 
-  static ThreadLocalKey kUnsetThreadLocalKey;
-  static ThreadId kInvalidThreadId;
-  static ThreadJoinId kInvalidThreadJoinId;
+  static const ThreadId kInvalidThreadId;
+  static const ThreadJoinId kInvalidThreadJoinId;
 
  private:
   // These methods should not be used in a generic way and hence
   // are private, they have been added to solve the problem of
   // accessing the VM thread structure from an OSThread object
   // in the windows thread interrupter which is used for profiling.
   // We could eliminate this requirement if the windows thread interrupter
   // is implemented differently.
   Thread* thread() const { return thread_; }
   void set_thread(Thread* value) {
@@ skipping 123 matching lines @@
 #endif  // defined(DEBUG)
 
   DISALLOW_COPY_AND_ASSIGN(Monitor);
 };
 
 
 }  // namespace dart
 
 
 #endif  // VM_OS_THREAD_H_