Only run pylint on Windows in PRESUBMIT

As a slight improvement for making changes on Windows, at least run
the pylint steps. The tests do not currently work with a variety of
failures, but at least running pylint would have caught the regressions
encountered here https://codereview.chromium.org/134313007/#msg19.

R=maruel@chromium.org
BUG=334953

Review URL: https://codereview.chromium.org/137243003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@245420 0039d316-1c4b-4281-b951-d872f2087c98

PRESUBMIT.py

@@ -23,21 +23,26 @@ def CommonChecks(input_api, output_api, tests_to_black_list):
     'R0401',  # Cyclic import
     'W0613',  # Unused argument
   ]
-  results.extend(input_api.RunTests(
-      input_api.canned_checks.GetPylint(
-          input_api,
-          output_api,
-          white_list=[r'.*\.py$'],
-          black_list=black_list,
-          disabled_warnings=disabled_warnings) +
-      # TODO(maruel): Make sure at least one file is modified first.
-      # TODO(maruel): If only tests are modified, only run them.
-      input_api.canned_checks.GetUnitTestsInDirectory(
-          input_api,
-          output_api,
-          'tests',
-          whitelist=[r'.*test\.py$'],
-          blacklist=tests_to_black_list)))
+  pylint = input_api.canned_checks.GetPylint(
+      input_api,
+      output_api,
+      white_list=[r'.*\.py$'],
+      black_list=black_list,
+      disabled_warnings=disabled_warnings)
+  # TODO(maruel): Make sure at least one file is modified first.
+  # TODO(maruel): If only tests are modified, only run them.
+  unit_tests = input_api.canned_checks.GetUnitTestsInDirectory(
+      input_api,
+      output_api,
+      'tests',
+      whitelist=[r'.*test\.py$'],
+      blacklist=tests_to_black_list)
+  tests = pylint
+  if not input_api.platform.startswith(('cygwin', 'win32')):
+    tests.extend(unit_tests)
+  else:
+    print('Warning: not running unit tests on Windows')
+  results.extend(input_api.RunTests(tests))
   return results