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

native_client_sdk/src/libraries/sdk_util/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_SDK_UTIL_REF_OBJECT
+#define LIBRARIES_SDK_UTIL_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_SDK_UTIL_REF_OBJECT
+