bpo-36084: Add native thread ID to threading.Thread objects (GH-11993)

diff --git a/Lib/threading.py b/Lib/threading.py
index 0ebbd67..3137e49 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -23,8 +23,8 @@
 # with the multiprocessing module, which doesn't provide the old
 # Java inspired names.
 
-__all__ = ['get_ident', 'active_count', 'Condition', 'current_thread',
-           'enumerate', 'main_thread', 'TIMEOUT_MAX',
+__all__ = ['get_ident', 'get_native_id', 'active_count', 'Condition',
+           'current_thread', 'enumerate', 'main_thread', 'TIMEOUT_MAX',
            'Event', 'Lock', 'RLock', 'Semaphore', 'BoundedSemaphore', 'Thread',
            'Barrier', 'BrokenBarrierError', 'Timer', 'ThreadError',
            'setprofile', 'settrace', 'local', 'stack_size']
@@ -34,6 +34,7 @@
 _allocate_lock = _thread.allocate_lock
 _set_sentinel = _thread._set_sentinel
 get_ident = _thread.get_ident
+get_native_id = _thread.get_native_id
 ThreadError = _thread.error
 try:
     _CRLock = _thread.RLock
@@ -790,6 +791,7 @@
         else:
             self._daemonic = current_thread().daemon
         self._ident = None
+        self._native_id = 0
         self._tstate_lock = None
         self._started = Event()
         self._is_stopped = False
@@ -891,6 +893,9 @@
     def _set_ident(self):
         self._ident = get_ident()
 
+    def _set_native_id(self):
+        self._native_id = get_native_id()
+
     def _set_tstate_lock(self):
         """
         Set a lock object which will be released by the interpreter when
@@ -903,6 +908,7 @@
         try:
             self._set_ident()
             self._set_tstate_lock()
+            self._set_native_id()
             self._started.set()
             with _active_limbo_lock:
                 _active[self._ident] = self
@@ -1077,6 +1083,17 @@
         assert self._initialized, "Thread.__init__() not called"
         return self._ident
 
+    @property
+    def native_id(self):
+        """Native integral thread ID of this thread or 0 if it has not been started.
+
+        This is a non-negative integer. See the get_native_id() function.
+        This represents the Thread ID as reported by the kernel.
+
+        """
+        assert self._initialized, "Thread.__init__() not called"
+        return self._native_id
+
     def is_alive(self):
         """Return whether the thread is alive.
 
@@ -1176,6 +1193,7 @@
         self._set_tstate_lock()
         self._started.set()
         self._set_ident()
+        self._set_native_id()
         with _active_limbo_lock:
             _active[self._ident] = self
 
@@ -1195,6 +1213,7 @@
 
         self._started.set()
         self._set_ident()
+        self._set_native_id()
         with _active_limbo_lock:
             _active[self._ident] = self