Fix pylint file list matching on Windows

Windows paths use backward slash separator, which
escapes regular expressions for white and black lists
in PRESUBMIT.py filters

See https://goo.gl/6c7aku for discussion

Bug:

Change-Id: Ia1d133c5b6cfa6cb364b1500b7b7abe583bce346
Reviewed-on: https://chromium-review.googlesource.com/461141
Commit-Queue: Marc-Antoine Ruel <maruel@chromium.org>
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>

presubmit_canned_checks.py

@@ -525,7 +525,8 @@ def GetUnitTestsInDirectory(
       continue
     unit_tests.append(input_api.os_path.join(directory, filename))
     to_run += 1
-  input_api.logging.debug('Found %d files, running %d' % (found, to_run))
+  input_api.logging.debug('Found %d files, running %d unit tests'
+                          % (found, to_run))
   if not to_run:
     return [
         output_api.PresubmitPromptWarning(
@@ -675,6 +676,9 @@ def _FetchAllFiles(input_api, white_list, black_list):
   # can break another unmodified file.
   # Use code similar to InputApi.FilterSourceFile()
   def Find(filepath, filters):
+    if input_api.platform == 'win32':
+      filepath = filepath.replace('\\', '/')
+
     for item in filters:
       if input_api.re.match(item, filepath):
         return True

tests/presubmit_unittest.py

@@ -2627,7 +2627,7 @@ class CannedChecksUnittest(PresubmitTestsBase):
         input_api,
         [presubmit.os.path.join('random_directory', 'b'), '--verbose'],
         cwd=self.fake_root_dir)
-    input_api.logging.debug('Found 5 files, running 1')
+    input_api.logging.debug('Found 5 files, running 1 unit tests')
 
     self.mox.ReplayAll()
     results = presubmit_canned_checks.RunUnitTestsInDirectory(