Add presubmit to run `{dm,nanobench}_flags.py test` when changed.

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 122 matching lines @@
   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 _ToolFlags(input_api, output_api):
+  """Make sure `{dm,nanobench}_flags.py test` passes if modified."""
+  results = []
+  sources = lambda x: ('dm_flags.py'        in x.LocalPath() or
+                       'nanobench_flags.py' in x.LocalPath())
+  for f in input_api.AffectedSourceFiles(sources):
+    if 0 != subprocess.call(['python', f.LocalPath(), 'test']):
+      results.append(output_api.PresubmitError('`python %s test` failed' % f))
+  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('.m') or
                        x.LocalPath().endswith('.mm') or
                        x.LocalPath().endswith('.go') or
                        x.LocalPath().endswith('.c') or
                        x.LocalPath().endswith('.cc') 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))
+  results.extend(_ToolFlags(input_api, output_api))
   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 291 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