Make CheckLicense() to not trigger on empty files.

presubmit_canned_checks.py

 # Copyright (c) 2010 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."""
 
 ### Description checks
 
 def CheckChangeHasTestField(input_api, output_api):
   """Requires that the changelist have a TEST= field."""
@@ skipping 257 matching lines @@
       if len(bad) == 5:  # Just show the first 5 errors.
         break
 
   if bad:
     msg = 'Found lines longer than %s characters (first 5 shown).' % maxlen
     return [output_api.PresubmitPromptWarning(msg, items=bad)]
   else:
     return []
 
 
-def CheckLicense(input_api, output_api, license, source_file_filter=None):
+def CheckLicense(input_api, output_api, license, source_file_filter=None,
+    accept_empty_files=True):
   """Verifies the license header.
   """
   license_re = input_api.re.compile(license, input_api.re.MULTILINE)
   bad_files = []
   for f in input_api.AffectedSourceFiles(source_file_filter):
     contents = input_api.ReadFile(f, 'rb')
+    if accept_empty_files and not contents:
+      continue
     if not license_re.search(contents):
       bad_files.append(f.LocalPath())
   if bad_files:
     if input_api.is_committing:
       res_type = output_api.PresubmitPromptWarning
     else:
       res_type = output_api.PresubmitNotifyResult
     return [res_type(
         'Found a bad license header in these files:', items=bad_files)]
   return []
@@ skipping 226 matching lines @@
     pending_builds_len = len(builder.get('pending_builds', []))
     if pending_builds_len > max_pendings:
       out.append('%s has %d build(s) pending' %
                   (builder_name, pending_builds_len))
   if out:
     return [output_api.PresubmitPromptWarning(
         'Build(s) pending. It is suggested to wait that no more than %d '
             'builds are pending.' % max_pendings,
         long_text='\n'.join(out))]
   return []