Fix pylint warnings in webkitpy/common/.

third_party/WebKit/Tools/Scripts/webkitpy/common/system/outputcapture.py

 # Copyright (c) 2009, 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 61 matching lines @@
     def restore_output(self):
         self._logger.removeHandler(self._logs_handler)
         self._logger.setLevel(self._orig_log_level)
         self._logs_handler.flush()
         self._logs.flush()
         logs_string = self._logs.getvalue()
         delattr(self, '_logs_handler')
         delattr(self, '_logs')
         return (self._restore_output_with_name("stdout"), self._restore_output_with_name("stderr"), logs_string)
 
-    def assert_outputs(self, testcase, function, args=[], kwargs={}, expected_stdout="",
+    def assert_outputs(self, testcase, function, args=None, kwargs=None, expected_stdout="",
                        expected_stderr="", expected_exception=None, expected_logs=None):
+        args = args or []
+        kwargs = kwargs or {}
         self.capture_output()
         try:
             if expected_exception:
                 return_value = testcase.assertRaises(expected_exception, function, *args, **kwargs)
             else:
                 return_value = function(*args, **kwargs)
         finally:
             (stdout_string, stderr_string, logs_string) = self.restore_output()
 
         if hasattr(testcase, 'assertMultiLineEqual'):
@@ skipping 21 matching lines @@
         del self.__captured_stdout
         del self.__captured_stderr
         self.output_capture.restore_output()
         unittest.TestCase.tearDown(self)
 
     def assertStdout(self, expected_stdout):
         self.assertEqual(expected_stdout, self.__captured_stdout.getvalue())
 
     def assertStderr(self, expected_stderr):
         self.assertEqual(expected_stderr, self.__captured_stderr.getvalue())