Fix pylint presubmit check so that it works on Windows.

presubmit_canned_checks.py

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Generic presubmit checks that can be reused by other presubmit checks."""
 
 import os as _os
 _HERE = _os.path.dirname(_os.path.abspath(__file__))
 
 
@@ skipping 625 matching lines @@
   extra_paths_list = extra_paths_list or []
 
   if input_api.is_committing:
     error_type = output_api.PresubmitError
   else:
     error_type = output_api.PresubmitPromptWarning
 
   # Only trigger if there is at least one python file affected.
   def rel_path(regex):
     """Modifies a regex for a subject to accept paths relative to root."""
-    if input_api.os_path.samefile(
-        input_api.PresubmitLocalPath(), input_api.change.RepositoryRoot()):
+    def samefile(a, b):
+      # Default implementation for platforms lacking os.path.samefile
+      # (like Windows).
+      return input_api.os_path.abspath(a) == input_api.os_path.abspath(b)
+    samefile = getattr(input_api.os_path, 'samefile', samefile)
+    if samefile(input_api.PresubmitLocalPath(),
+                input_api.change.RepositoryRoot()):
       return regex
+
     prefix = input_api.os_path.join(input_api.os_path.relpath(
         input_api.PresubmitLocalPath(), input_api.change.RepositoryRoot()), '')
     return input_api.re.escape(prefix) + regex
   src_filter = lambda x: input_api.FilterSourceFile(
       x, map(rel_path, white_list), map(rel_path, black_list))
   if not input_api.AffectedSourceFiles(src_filter):
     input_api.logging.info('Skipping pylint: no matching changes.')
     return []
 
   extra_args = ['--rcfile=%s' % input_api.os_path.join(_HERE, 'pylintrc')]
@@ skipping 340 matching lines @@
     snapshot("checking description")
     results.extend(input_api.canned_checks.CheckChangeHasDescription(
         input_api, output_api))
     results.extend(input_api.canned_checks.CheckDoNotSubmitInDescription(
         input_api, output_api))
     snapshot("checking do not submit in files")
     results.extend(input_api.canned_checks.CheckDoNotSubmitInFiles(
         input_api, output_api))
   snapshot("done")
   return results