Makefiles will always contain tabs so make the notab check filter them out.

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 195 matching lines @@
     outputs.append(output_api.PresubmitPromptWarning(
       'These files should end in one (and only one) newline character:',
       items=eof_files))
   return outputs
 
 
 def CheckChangeHasNoTabs(input_api, output_api, source_file_filter=None):
   """Checks that there are no tab characters in any of the text files to be
   submitted.
   """
+  # In addition to the filter, make sure that makefiles are blacklisted.
+  if not source_file_filter:
+    # It's the default filter.
+    source_file_filter = input_api.FilterSourceFile
+  def filter_more(affected_file):
+    return (not input_api.os_path.basename(affected_file.LocalPath()) in
+                ('Makefile', 'makefile') and
+            source_file_filter(affected_file))
   tabs = []
-  for f, line_num, line in input_api.RightHandSideLines(source_file_filter):
+  for f, line_num, line in input_api.RightHandSideLines(filter_more):
     if '\t' in line:
       tabs.append('%s, line %s' % (f.LocalPath(), line_num))
   if tabs:
     return [output_api.PresubmitPromptWarning('Found a tab character in:',
                                               long_text='\n'.join(tabs))]
   return []
 
 
 def CheckChangeHasNoStrayWhitespace(input_api, output_api,
                                     source_file_filter=None):
@@ skipping 260 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 []