Don't run checkstyle on non-source-code.

PRESUBMIT.py

 # 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.
 
 """Top-level presubmit script for Chromium.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
@@ skipping 1200 matching lines @@
   try:
     sys.path = sys.path + [input_api.os_path.join(
         input_api.PresubmitLocalPath(), 'tools', 'android', 'checkstyle')]
     import checkstyle
   finally:
     # Restore sys.path to what it was before.
     sys.path = original_sys_path
 
   return checkstyle.RunCheckstyle(
       input_api, output_api, 'tools/android/checkstyle/chromium-style-5.0.xml',
-      black_list=_EXCLUDED_PATHS)
+      black_list=_EXCLUDED_PATHS + input_api.DEFAULT_BLACK_LIST)
 
 
 def _CheckForCopyrightedCode(input_api, output_api):
   """Verifies that newly added code doesn't contain copyrighted material
   and is properly licensed under the standard Chromium license.
 
   As there can be false positives, we maintain a whitelist file. This check
   also verifies that the whitelist file is up to date.
   """
   import sys
@@ skipping 461 matching lines @@
         if 'presubmit' in builder:
           builders[master].pop(builder)
 
   # Match things like path/aura/file.cc and path/file_aura.cc.
   # Same for chromeos.
   if any(re.search(r'[\\\/_](aura|chromeos)', f) for f in files):
     tryserver_linux = builders.setdefault('tryserver.chromium.linux', {})
     tryserver_linux['linux_chromium_chromeos_asan_rel_ng'] = ['defaulttests']
 
   return builders