Fix confidence check and problems with successive builds due to symlinks.

tools/auto_bisect/bisect_utils.py

 # Copyright 2014 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.
 
 """Utility functions used by the bisect tool.
 
 This includes functions related to checking out the depot and outputting
 annotations for the Buildbot waterfall.
 """
 
@@ skipping 457 matching lines @@
       _CleanupPreviousGitRuns(path_to_dir)
       # Checks out the master branch, throws an exception if git command fails.
       CheckRunGit(['checkout', '-f', 'master'], cwd=path_to_dir)
   if not _CreateAndChangeToSourceDirectory(opts.working_directory):
     raise RuntimeError('Could not create bisect directory.')
 
   if not SetupGitDepot(opts, custom_deps):
     raise RuntimeError('Failed to grab source.')
 
 
-def RunProcess(command):
+def RunProcess(command, cwd=None, shell=False):
   """Runs an arbitrary command.
 
   If output from the call is needed, use RunProcessAndRetrieveOutput instead.
 
   Args:
     command: A list containing the command and args to execute.
 
   Returns:
     The return code of the call.
   """
   # On Windows, use shell=True to get PATH interpretation.
-  shell = IsWindowsHost()
-  return subprocess.call(command, shell=shell)
+  shell = shell or IsWindowsHost()
+  return subprocess.call(command, cwd=cwd, shell=shell)
 
 
 def RunProcessAndRetrieveOutput(command, cwd=None):
   """Runs an arbitrary command, returning its output and return code.
 
   Since output is collected via communicate(), there will be no output until
   the call terminates. If you need output while the program runs (ie. so
   that the buildbot doesn't terminate the script), consider RunProcess().
 
   Args:
@@ skipping 52 matching lines @@
     platform = os.environ.get('PROCESSOR_ARCHITECTURE')
   return platform and platform in ['AMD64', 'I64']
 
 
 def IsLinuxHost():
   return sys.platform.startswith('linux')
 
 
 def IsMacHost():
   return sys.platform.startswith('darwin')