Added regexp-re2 library to external.

Change-Id: I54e60045f0fee91b64e4d7291e5bb6c6cffb4562
diff --git a/util/thread.h b/util/thread.h
new file mode 100644
index 0000000..b9610e0
--- /dev/null
+++ b/util/thread.h
@@ -0,0 +1,26 @@
+// Copyright 2009 The RE2 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 RE2_UTIL_THREAD_H__
+#define RE2_UTIL_THREAD_H__
+
+#include <pthread.h>
+
+class Thread {
+ public:
+  Thread();
+  virtual ~Thread();
+  void Start();
+  void Join();
+  void SetJoinable(bool);
+  virtual void Run() = 0;
+ 
+ private:
+  pthread_t pid_;
+  bool running_;
+  bool joinable_;
+};
+
+#endif  // RE2_UTIL_THREAD_H__
+