Fix all "dangerous-default-value" pylint warnings.

third_party/WebKit/Tools/Scripts/webkitpy/style/error_handlers_unittest.py

 # Copyright (C) 2010 Chris Jerdonek (cjerdonek@webkit.org)
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions
 # are met:
 # 1.  Redistributions of source code must retain the above copyright
 #     notice, this list of conditions and the following disclaimer.
 # 2.  Redistributions in binary form must reproduce the above copyright
 #     notice, this list of conditions and the following disclaimer in the
 #     documentation and/or other materials provided with the distribution.
@@ skipping 72 matching lines @@
         """Test the __eq__() method for the return value of True."""
         handler1 = self._error_handler(configuration=None)
         handler2 = self._error_handler(configuration=None)
 
         self.assertTrue(handler1.__eq__(handler2))
 
     def test_eq__false_return_value(self):
         """Test the __eq__() method for the return value of False."""
         def make_handler(configuration=self._style_checker_configuration(),
                          file_path='foo.txt', increment_error_count=lambda: True,
-                         line_numbers=[100]):
+                         line_numbers=None):
+            line_numbers = line_numbers or [100]
             return DefaultStyleErrorHandler(configuration=configuration,
                                             file_path=file_path,
                                             increment_error_count=increment_error_count,
                                             line_numbers=line_numbers)
 
         handler = make_handler()
 
         # Establish a baseline for our comparisons below.
         self.assertTrue(handler.__eq__(make_handler()))
 
@@ skipping 82 matching lines @@
                          ["foo.h(50):  message  [whitespace/tab] [5]\n"])
 
         # Error on non-modified line after turning off line filtering: error.
         error_handler.turn_off_line_filtering()
         self._call_error_handler(error_handler, confidence, line_number=60)
         self.assertEqual(2, self._error_count)
         self.assertEqual(self._error_messages,
                          ['foo.h(50):  message  [whitespace/tab] [5]\n',
                           'foo.h(60):  message  [whitespace/tab] [5]\n',
                           'Suppressing further [whitespace/tab] reports for this file.\n'])