[WebUI] Make CSS presubmit play nice with grit XML.

chrome/browser/resources/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.
 
 """Presubmit script for Chromium WebUI resources.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl/git cl, and see
 http://www.chromium.org/developers/web-development-style-guide for the rules
 we're checking against here.
 """
 
 
 def CheckChangeOnUpload(input_api, output_api):
   return _CommonChecks(input_api, output_api)
 
 
 def CheckChangeOnCommit(input_api, output_api):
   return _CommonChecks(input_api, output_api)
 
 
 def _CommonChecks(input_api, output_api):
   """Checks common to both upload and commit."""
   results = []
   resources = input_api.PresubmitLocalPath()
 
   path = input_api.os_path
-  presubmit = path.join(resources, 'PRESUBMIT.py')
-  if presubmit in (f.AbsoluteLocalPath() for f in input_api.AffectedFiles()):
+  affected_files = (f.AbsoluteLocalPath() for f in input_api.AffectedFiles())
+  would_affect_tests = (
+      path.join(resources, 'PRESUBMIT.py'),
+      path.join(resources, 'test_presubmit.py'),
+      path.join(resources, 'web_dev_style', 'css_checker.py'),
+      path.join(resources, 'web_dev_style', 'js_checker.py'),
+  )
+  if any(f for f in affected_files if f in would_affect_tests):
     tests = [path.join(resources, 'test_presubmit.py')]
     results.extend(
         input_api.canned_checks.RunUnitTests(input_api, output_api, tests))
 
   import sys
   old_path = sys.path
 
   try:
     sys.path.insert(0, resources)
     from web_dev_style import css_checker, js_checker
@@ skipping 10 matching lines @@
       return (f.startswith(dirs) and f.endswith(('.css', '.html', '.js')))
 
     results.extend(css_checker.CSSChecker(input_api, output_api,
                                           file_filter=file_filter).RunChecks())
     results.extend(js_checker.JSChecker(input_api, output_api,
                                         file_filter=file_filter).RunChecks())
   finally:
     sys.path = old_path
 
   return results