GTTF: always run perf tests serially

chrome/test/base/browser_perf_tests_main.cc

 // Copyright 2013 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/sys_info.h"
 #include "chrome/test/base/chrome_test_launcher.h"
 
 int main(int argc, char** argv) {
-  int default_jobs = std::max(1, base::SysInfo::NumberOfProcessors() / 2);
-  return LaunchChromeTests(default_jobs, argc, argv);
+  // Always run browser perf tests serially - parallel running would be less
+  // deterministic and distort perf measurements.
+  return LaunchChromeTests(1, argc, argv);
 }