volatile -> const, where possible

runtime/vm/thread.h

 // Copyright (c) 2015, 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_THREAD_H_
 #define VM_THREAD_H_
 
 #include "vm/base_isolate.h"
 #include "vm/globals.h"
 #include "vm/os_thread.h"
 
 namespace dart {
 
 class CHA;
 class Isolate;
 
 // A VM thread; may be executing Dart code or performing helper tasks like
 // garbage collection or compilation.
 class Thread {
  public:
   explicit Thread(Isolate* isolate)
       : isolate_(isolate),
         cha_(NULL) {}
 
   static void InitOnce();
 
   static Thread* Current() {
-    return reinterpret_cast<Thread*>(OSThread::GetThreadLocal(thread_key));
+    return reinterpret_cast<Thread*>(OSThread::GetThreadLocal(thread_key_));
   }
   static void SetCurrent(Thread* current);
 
   // The topmost zone used for allocation in this thread.
   Zone* zone() {
     return reinterpret_cast<BaseIsolate*>(isolate())->current_zone();
   }
 
   // The isolate that this thread is operating on, or NULL if none.
   Isolate* isolate() const { return isolate_; }
 
   // The (topmost) CHA for the compilation in this thread.
   CHA* cha() const { return cha_; }
   void set_cha(CHA* value) { cha_ = value; }
 
  private:
-  static ThreadLocalKey thread_key;
+  static ThreadLocalKey thread_key_;
 
   Isolate* isolate_;
   CHA* cha_;
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 }  // namespace dart
 
 #endif  // VM_THREAD_H_