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

runtime/bin/thread_pool_macos.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 <pthread.h>
-
-#include "bin/thread_pool.h"
-
-void ThreadPool::Start() {
-  pthread_t* threads
-      = reinterpret_cast<pthread_t*>(calloc(size_, sizeof(pthread_t*)));  // NOLINT
-  data_.set_threads(threads);
-  for (int i = 0; i < size_; i++) {
-    pthread_t handler_thread;
-    int result = pthread_create(&handler_thread,
-                                NULL,
-                                &ThreadPool::Main,
-                                this);
-    if (result != 0) {
-      FATAL("Create and start thread pool thread");
-    }
-    data_.threads()[i] = handler_thread;
-  }
-}
-
-
-void ThreadPool::Shutdown() {
-  terminate_ = true;
-  queue_.Shutdown();
-  for (int i = 0; i < size_; i++) {
-    pthread_join(data_.threads()[i], NULL);
-  }
-}