Update Native Client Authors to be Chromium Authors for the code moved from the

ppapi/native_client/src/shared/ppapi_proxy/plugin_threading.cc

 /*
- * Copyright (c) 2011 The Native Client Authors. All rights reserved.
+ * Copyright (c) 2011 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 <pthread.h>
 
 #include "native_client/src/include/nacl_macros.h"
 #include "native_client/src/shared/ppapi_proxy/ppruntime.h"
 
 
@@ skipping 22 matching lines @@
 }
 
 const static struct PP_ThreadFunctions thread_funcs = {
   thread_create,
   thread_join
 };
 
 void PpapiPluginRegisterDefaultThreadCreator() {
   PpapiPluginRegisterThreadCreator(&thread_funcs);
 }