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

third_party/WebKit/Tools/Scripts/webkitpy/style/checkers/cpp_unittest.py

 # -*- coding: utf-8; -*-
 #
 # Copyright (C) 2011 Google Inc. All rights reserved.
 # Copyright (C) 2009 Torch Mobile Inc.
 # Copyright (C) 2009 Apple Inc. All rights reserved.
 # 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:
@@ skipping 2061 matching lines @@
     def test_mixing_unsigned_bool_bitfields(self):
         def errmsg(bool_bitfields, unsigned_bitfields, name):
             bool_list = ', '.join(bool_bitfields)
             unsigned_list = ', '.join(unsigned_bitfields)
             return ('The class %s contains mixed unsigned and bool bitfields, '
                     'which will pack into separate words on the MSVC compiler.\n'
                     'Bool bitfields are [%s].\nUnsigned bitfields are [%s].\n'
                     'Consider converting bool bitfields to unsigned.  [runtime/bitfields] [5]'
                     % (name, bool_list, unsigned_list))
 
-        def build_test_case(bitfields, name, will_warn, extra_warnings=[]):
+        def build_test_case(bitfields, name, will_warn, extra_warnings=None):
             bool_bitfields = []
             unsigned_bitfields = []
             test_string = 'class %s {\n' % (name,)
             line = 2
             for bitfield in bitfields:
                 test_string += '    %s %s : %d;\n' % bitfield
                 if bitfield[0] == 'bool':
                     bool_bitfields.append('%d: %s' % (line, bitfield[1]))
                 elif bitfield[0].startswith('unsigned'):
                     unsigned_bitfields.append('%d: %s' % (line, bitfield[1]))
@@ skipping 2042 matching lines @@
     def test_ne(self):
         """Test __ne__ inequality function."""
         checker1 = self._checker()
         checker2 = self._checker()
 
         # != calls __ne__.
         # By default, __ne__ always returns true on different objects.
         # Thus, just check the distinguishing case to verify that the
         # code defines __ne__.
         self.assertFalse(checker1 != checker2)