webkitpy: Make webkit_base() protected.

third_party/WebKit/Tools/Scripts/webkitpy/performance_tests/perftestsrunner.py

 # Copyright (C) 2012 Google Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 45 matching lines @@
     _DEFAULT_JSON_FILENAME = 'PerformanceTestsResults.json'
 
     def __init__(self, args=None, port=None):
         self._options, self._args = PerfTestsRunner._parse_args(args)
         if port:
             self._port = port
             self._host = self._port.host
         else:
             self._host = Host()
             self._port = self._host.port_factory.get(self._options.platform, self._options)
-        self._webkit_base_dir_len = len(self._port.webkit_base())
         self._base_path = self._port.perf_tests_dir()
         self._timestamp = time.time()
         self._utc_timestamp = datetime.datetime.utcnow()
 
     @staticmethod
     def _parse_args(args=None):
         def _expand_path(option, opt_str, value, parser):
             path = os.path.expandvars(os.path.expanduser(value))
             setattr(parser.values, option.dest, path)
         perf_option_list = [
@@ skipping 294 matching lines @@
             if metrics:
                 self._results.append((test, metrics))
             else:
                 failures += 1
                 _log.error('FAILED')
 
             _log.info('Finished: %f s', time.time() - start_time)
             _log.info('')
 
         return failures