Add presubmit check for copyright notice

PRESUBMIT.py

 # Copyright (c) 2013 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.
 
 
 """Top-level presubmit script for Skia.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
@@ skipping 100 matching lines @@
   results = []
   if failing_files:
     results.append(
         output_api.PresubmitError(
             'The following files have #if or #ifdef before includes:\n%s\n\n'
             'See skbug.com/3362 for why this should be fixed.' %
                 '\n'.join(failing_files)))
   return results
 
 
+def _CopyrightChecks(input_api, output_api, source_file_filter=None):
+  results = []
+  year_pattern = r'\d{4}'
+  year_range_pattern = r'%s(-%s)?' % (year_pattern, year_pattern)
+  years_pattern = r'%s(,%s)*,?' % (year_range_pattern, year_range_pattern)
+  copyright_pattern = (
+      r'Copyright (\([cC]\) )?%s \w+' % years_pattern)
+
+  for affected_file in input_api.AffectedSourceFiles(source_file_filter):
+    if 'third_party' in affected_file.LocalPath():
+      continue
+    contents = input_api.ReadFile(affected_file, 'rb')
+    if not re.search(copyright_pattern, contents):
+      results.append(output_api.PresubmitError(
+          '%s is missing a correct copyright header.' % affected_file))
+  return results
+
+
 def _CommonChecks(input_api, output_api):
   """Presubmit checks common to upload and commit."""
   results = []
   sources = lambda x: (x.LocalPath().endswith('.h') or
                        x.LocalPath().endswith('.gypi') or
                        x.LocalPath().endswith('.gyp') or
                        x.LocalPath().endswith('.py') or
                        x.LocalPath().endswith('.sh') or
                        x.LocalPath().endswith('.cpp'))
   results.extend(
       _CheckChangeHasEol(
           input_api, output_api, source_file_filter=sources))
   results.extend(_PythonChecks(input_api, output_api))
   results.extend(_IfDefChecks(input_api, output_api))
+  results.extend(_CopyrightChecks(input_api, output_api,
+                                  source_file_filter=sources))
   return results
 
 
 def CheckChangeOnUpload(input_api, output_api):
   """Presubmit checks for the change on upload.
 
   The following are the presubmit checks:
   * Check change has one and only one EOL.
   """
   results = []
@@ skipping 235 matching lines @@
     state and an error if it is in 'Closed' state.
   """
   results = []
   results.extend(_CommonChecks(input_api, output_api))
   results.extend(
       _CheckTreeStatus(input_api, output_api, json_url=(
           SKIA_TREE_STATUS_URL + '/banner-status?format=json')))
   results.extend(_CheckLGTMsForPublicAPI(input_api, output_api))
   results.extend(_CheckOwnerIsInAuthorsFile(input_api, output_api))
   return results