Change the thread interface in runtime/platform and use it starting all threads

runtime/platform/thread_macos.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 PLATFORM_THREAD_MACOS_H_
 #define PLATFORM_THREAD_MACOS_H_
 
 #if !defined(PLATFORM_THREAD_H_)
 #error Do not include thread_macos.h directly; use thread.h instead.
 #endif
 
 #include <pthread.h>
 
 #include "platform/globals.h"
 
 namespace dart {
 
-class ThreadData {
- private:
-  ThreadData() {}
-  ~ThreadData() {}
-
-  pthread_t* tid() { return &tid_; }
-
-  pthread_t tid_;
-
-  friend class Thread;
-
-  DISALLOW_ALLOCATION();
-  DISALLOW_COPY_AND_ASSIGN(ThreadData);
-};
-
+typedef pthread_t ThreadHandle;
 
 class MutexData {
  private:
   MutexData() {}
   ~MutexData() {}
 
   pthread_mutex_t* mutex() { return &mutex_; }
 
   pthread_mutex_t mutex_;
 
@@ skipping 17 matching lines @@
 
   friend class Monitor;
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(MonitorData);
 };
 
 }  // namespace dart
 
 #endif  // PLATFORM_THREAD_MACOS_H_