Fix check_package_boundaries presubmit test for Windows.

tools-webrtc/check_package_boundaries_test.py

Index: tools-webrtc/check_package_boundaries_test.py
diff --git a/tools-webrtc/check_package_boundaries_test.py b/tools-webrtc/check_package_boundaries_test.py
index 437f6e6eac69b73e21830e6fac817475d2b4e2f1..c59c4850b3dbf3616e8f4a3cad0bebcb7f3e3fde 100755
--- a/tools-webrtc/check_package_boundaries_test.py
+++ b/tools-webrtc/check_package_boundaries_test.py
@@ -33,6 +33,7 @@ class Logger(object):
   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])