Move thread_pool.h into utils so it can be shared by more than one example.

native_client_sdk/src/libraries/utils/ref_object.h

-/* Copyright (c) 2012 The Chromium Authors. All rights reserved.
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef LIBRARIES_UTILS_REF_OBJECT
-#define LIBRARIES_UTILS_REF_OBJECT
-
-#include <stdlib.h>
-#include "pthread.h"
-
-class RefObject {
- public:
-  RefObject() {
-    ref_count_ = 1;
-    pthread_mutex_init(&lock_, NULL);
-  }
-
-  int RefCount() const { return ref_count_; }
-
-  void Acquire() {
-    ref_count_++;
-  }
-
-  bool Release() {
-    if (--ref_count_ == 0) {
-      Destroy();
-      delete this;
-      return false;
-    }
-    return true;
-  }
-
- protected:
-  virtual ~RefObject() {
-    pthread_mutex_destroy(&lock_);
-  }
-
-  // Override to clean up object when last reference is released.
-  virtual void Destroy() {}
-
-  pthread_mutex_t lock_;
-
- private:
-  int ref_count_;
-};
-
-#endif  // LIBRARIES_UTILS_REF_OBJECT