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

Tools/Scripts/webkitpy/common/checkout/baselineoptimizer_unittest.py

 # Copyright (C) 2011 Google Inc. All rights reserved.
 #
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 # 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
 # in the documentation and/or other materials provided with the
 # distribution.
 #    * Neither the name of Google Inc. nor the names of its
 # contributors may be used to endorse or promote products derived from
 # this software without specific prior written permission.
 #
 # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 # "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 # LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 # A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 # OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 # LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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-import webkitpy.thirdparty.unittest2 as unittest
+import unittest
 
 from webkitpy.common.checkout.baselineoptimizer import BaselineOptimizer
 from webkitpy.common.checkout.scm.scm_mock import MockSCM
 from webkitpy.common.host_mock import MockHost
 from webkitpy.common.webkit_finder import WebKitFinder
 
 
 class ExcludingMockSCM(MockSCM):
     def __init__(self, exclusion_list, filesystem=None, executive=None):
         MockSCM.__init__(self, filesystem, executive)
@@ skipping 231 matching lines @@
         host=MockHost(scm=ExcludingMockSCM(['/mock-checkout/third_party/WebKit/LayoutTests/virtual/softwarecompositing/mock-baseline-expected.txt'])))
 
     def test_virtual_root_not_redundant_with_ancestors(self):
         self._assertOptimization({
             'virtual/softwarecompositing': '2',
             'platform/mac/compositing': '1',
         }, {
             'virtual/softwarecompositing': '2',
             'platform/mac/compositing': '1',
         }, baseline_dirname='virtual/softwarecompositing')