Don't set goma_dir in config if path_to_goma is None.

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 try bot 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 336 matching lines @@
     config: The config read from run-perf-test.cfg.
     path_to_file: Path to the bisect-perf-regression.py script.
     path_to_goma: Path to goma directory.
 
   Returns:
     The exit code of bisect-perf-regression.py: 0 on success, otherwise 1.
   """
   try:
     with Goma(path_to_goma) as _:
       config['use_goma'] = bool(path_to_goma)
-      config['goma_dir'] = os.path.abspath(path_to_goma)
+      if config['use_goma']:
+        config['goma_dir'] = os.path.abspath(path_to_goma)
       _RunPerformanceTest(config, path_to_file)
     return 0
   except RuntimeError, e:
     bisect_utils.OutputAnnotationStepClosed()
     _OutputFailedResults('Error: %s' % e.message)
     return 1
 
 
 def _RunBisectionScript(
     config, working_directory, path_to_file, path_to_goma, path_to_extra_src,
@@ skipping 197 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())