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

ppapi/native_client/src/shared/ppapi_proxy/proxy_var.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 "native_client/src/shared/ppapi_proxy/proxy_var.h"
 
 #include "native_client/src/shared/platform/nacl_sync_checked.h"
 #include "native_client/src/untrusted/pthread/pthread.h"
 
 #include <limits>
 
 namespace ppapi_proxy {
 
 namespace {
 
 pthread_mutex_t mu = PTHREAD_MUTEX_INITIALIZER;
 
 }  // namespace
 
 int64_t ProxyVar::unique_var_id = 0;
 
 ProxyVar::ProxyVar(PP_VarType pp_var_type) : pp_var_type_(pp_var_type) {
   // Roll id of INT64_MAX to 1, because an id of 0 is not valid.
   nacl::ScopedPthreadMutexLock ml(&mu);
   if (unique_var_id > std::numeric_limits<int64_t>::max() - 1)
     unique_var_id = 0;
   id_ = ++unique_var_id;
 }
 
 }  // namespace ppapi_proxy