Exclude .md files from version control conflict detection.

PRESUBMIT_test.py

 #!/usr/bin/env python
 # 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.
 
 import glob
 import json
 import os
 import re
 import subprocess
@@ skipping 252 matching lines @@
              '=======',
              '  ScopedTempDir temp_dir_;',
              '>>>>>>> master']
     errors = PRESUBMIT._CheckForVersionControlConflictsInFile(
         MockInputApi(), MockFile('some/path/foo_platform.cc', lines))
     self.assertEqual(3, len(errors))
     self.assertTrue('1' in errors[0])
     self.assertTrue('3' in errors[1])
     self.assertTrue('5' in errors[2])
 
+  def testIgnoresReadmes(self):
+    lines = ['A First Level Header',
+             '====================',
+             '',
+             'A Second Level Header',
+             '---------------------']
+    errors = PRESUBMIT._CheckForVersionControlConflictsInFile(
+        MockInputApi(), MockFile('some/polymer/README.md', lines))
+    self.assertEqual(0, len(errors))
+
 class UmaHistogramChangeMatchedOrNotTest(unittest.TestCase):
   def testTypicalCorrectlyMatchedChange(self):
     diff_cc = ['UMA_HISTOGRAM_BOOL("Bla.Foo.Dummy", true)']
     diff_xml = ['<histogram name="Bla.Foo.Dummy"> </histogram>']
     mock_input_api = MockInputApi()
     mock_input_api.files = [
       MockFile('some/path/foo.cc', diff_cc),
       MockFile('tools/metrics/histograms/histograms.xml', diff_xml),
     ]
     warnings = PRESUBMIT._CheckUmaHistogramChanges(mock_input_api,
@@ skipping 562 matching lines @@
         mock_input_api, mock_output_api)
 
     self.assertEqual(1, len(warnings))
     self.assertEqual(2, len(warnings[0].items))
     self.assertTrue('HasAndroidLog.java' in warnings[0].items[0])
     self.assertTrue('HasExplicitLog.java' in warnings[0].items[1])
 
 
 if __name__ == '__main__':
   unittest.main()