Use Welch's t-test to calculate confidence scores in the bisect script.

tools/run-bisect-perf-regression.py

 #!/usr/bin/env python
 # Copyright (c) 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.
 
 """Run Performance Test Bisect Tool
 
 This script is used by a trybot to run the src/tools/bisect-perf-regression.py
 script with the parameters specified in run-bisect-perf-regression.cfg. It will
 check out a copy of the depot in a subdirectory 'bisect' of the working
@@ skipping 73 matching lines @@
     # since it will return an error if it wasn't running.
     self._Stop()
 
     if subprocess.call([self._abs_path_to_goma_file, 'start']):
       raise RuntimeError('Goma failed to start.')
 
   def _Stop(self):
     subprocess.call([self._abs_path_to_goma_file, 'stop'])
 
 
-def _LoadConfigFile(config_file_path):
-  """Loads the given file as a python module and returns the config dictionary.
-
-  The config file is loaded as a Python module.
+def _LoadConfigFile(path_to_file):
+  """Attempts to load the specified config file as a module
+  and grab the global config dict.
 
   Args:
     config_file_path: Path to the config file.
 
   Returns:
     If successful, returns the config dict loaded from the file. If no
     such dictionary could be loaded, returns the empty dictionary.
   """
   try:
     local_vars = {}
@@ skipping 443 matching lines @@
           config, current_dir, opts.path_to_goma)
 
   print ('Error: Could not load config file. Double check your changes to '
          'run-bisect-perf-regression.cfg or run-perf-test.cfg for syntax '
          'errors.\n')
   return 1
 
 
 if __name__ == '__main__':
   sys.exit(main())