Don't use statically declared Mutex in debugger

runtime/bin/dbg_message.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 BIN_DBG_MESSAGE_H_
 #define BIN_DBG_MESSAGE_H_
 
 #include "bin/builtin.h"
 #include "bin/utils.h"
 
@@ skipping 237 matching lines @@
   static void IsolateEventHandler(Dart_IsolateId isolate_id,
                                   Dart_IsolateEvent kind);
 
   // Print list of isolate ids of all message queues into text buffer.
   static void ListIsolateIds(dart::TextBuffer* msg);
 
  private:
   static DbgMsgQueue* GetIsolateMsgQueueLocked(Dart_IsolateId isolate_id);
 
   static DbgMsgQueue* list_;
-  static dart::Mutex msg_queue_list_lock_;
+  static dart::Mutex* msg_queue_list_lock_;
 
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(DbgMsgQueueList);
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_DBG_MESSAGE_H_