Fix check_package_boundaries presubmit test for Windows.

tools-webrtc/check_package_boundaries_test.py

 #!/usr/bin/env python
 
 # Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
@@ skipping 15 matching lines @@
 
 
 class Logger(object):
   def __init__(self, test_dir):
     self.messages = []
     self.test_dir = test_dir
 
   def log(self, build_file_path, line_number, target_name, source_file,
           subpackage):
     build_file_path = os.path.relpath(build_file_path, self.test_dir)
+    build_file_path = build_file_path.replace(os.path.sep, '/')
     self.messages.append([build_file_path, line_number, target_name,
                           source_file, subpackage])
 
 
 class UnitTest(unittest.TestCase):
   def RunTest(self, test_dir, check_all_build_files=False):
     logger = Logger(test_dir)
     build_files = [os.path.join(test_dir, 'BUILD.gn')]
     if check_all_build_files:
       build_files = None
@@ skipping 12 matching lines @@
 
   def test_common_prefix(self):
     self.RunTest(os.path.join(TESTDATA_DIR, 'common_prefix'))
 
   def test_all_build_files(self):
     self.RunTest(os.path.join(TESTDATA_DIR, 'all_build_files'), True)
 
 
 if __name__ == '__main__':
   unittest.main()