Overhaul microbenchmark so that it can be pulled in easily by any package

src/platform/minijail/getpid_microbenchmark.cc

 // Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-// Some portions Copyright (c) 2009 The Chromium Authors.
 //
 // Microbenchmark of getpid()
 #include "microbenchmark/microbenchmark.h"
 
 #include <syscall.h>
 namespace chromeos {
 namespace benchmarks {
 
 static void GetPid(bool scaffold_only) {
   if (!scaffold_only) syscall(__NR_getpid);
 }
 CHROMEOS_MICROBENCHMARK(GetPid, 1000000);
 
 }  // namespace benchmarks
 }  // namespace chromeos