Remove thirdparty/unittest2 from webkitpy and require python2.7.

Tools/Scripts/webkitpy/layout_tests/breakpad/dump_reader_multipart_unittest.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
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 # modification, are permitted provided that the following conditions are
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 #     * Redistributions of source code must retain the above copyright
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 #     * Redistributions in binary form must reproduce the above
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 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 import cgi
 
 from webkitpy.common.host_mock import MockHost
 from webkitpy.common.system.executive_mock import MockExecutive
 from webkitpy.layout_tests.breakpad.dump_reader_multipart import DumpReaderMultipart
 
 
 class TestDumpReaderMultipart(unittest.TestCase):
     _MULTIPART_DUMP = [
@@ skipping 60 matching lines @@
         dump_reader._file_extension = lambda: 'dmp'
         dump_reader._binaries_to_symbolize = lambda: ['content_shell']
 
         self.assertTrue(dump_reader.check_is_functional())
         self.assertEqual("MOCK output of child process", dump_reader._get_stack_from_dump(dump_file))
         self.assertEqual(2, len(host.executive.calls))
         cmd_line = " ".join(host.executive.calls[0])
         self.assertIn('generate_breakpad_symbols.py', cmd_line)
         cmd_line = " ".join(host.executive.calls[1])
         self.assertIn('minidump_stackwalk', cmd_line)