mach_port_deallocate() the result of mach_thread_self(), which obtains a port send right.

base/threading/platform_thread_posix.cc

 // 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.
 
 #include "base/threading/platform_thread.h"
 
 #include <errno.h>
 #include <sched.h>
 
 #include "base/lazy_instance.h"
@@ skipping 115 matching lines @@
   return success;
 }
 
 }  // namespace
 
 // static
 PlatformThreadId PlatformThread::CurrentId() {
   // Pthreads doesn't have the concept of a thread ID, so we have to reach down
   // into the kernel.
 #if defined(OS_MACOSX)
-  return mach_thread_self();
+  mach_port_t port = mach_thread_self();
+  mach_port_deallocate(mach_task_self(), port);
+  return port;
 #elif defined(OS_LINUX)
   return syscall(__NR_gettid);
 #elif defined(OS_ANDROID)
   return gettid();
 #elif defined(OS_NACL) || defined(OS_SOLARIS)
   return pthread_self();
 #elif defined(OS_POSIX)
   return reinterpret_cast<int64>(pthread_self());
 #endif
 }
@@ skipping 103 matching lines @@
 // Mac OS X uses lower-level mach APIs
 
 // static
 void PlatformThread::SetThreadPriority(PlatformThreadHandle, ThreadPriority) {
   // TODO(crogers): implement
   NOTIMPLEMENTED();
 }
 #endif
 
 }  // namespace base