Add pylint presubmit check.

PRESUBMIT.py

 # Copyright (c) 2011 Google Inc. 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 GYP.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
@@ skipping 16 matching lines @@
   ) % {
       'year': input_api.time.strftime('%Y'),
   }
 
   report.extend(input_api.canned_checks.PanProjectChecks(
       input_api, output_api, license_header=license))
   report.extend(input_api.canned_checks.CheckTreeIsOpen(
       input_api, output_api,
       'http://gyp-status.appspot.com/status',
       'http://gyp-status.appspot.com/current'))
+
+  import sys
+  old_sys_path = sys.path
+  try:
+    sys.path = ['pylib', 'test/lib'] + sys.path
+    report.extend(input_api.canned_checks.RunPylint(
+        input_api,
+        output_api))
+  finally:
+    sys.path = old_sys_path
   return report
 
 
 def GetPreferredTrySlaves():
   return ['gyp-win32', 'gyp-win64', 'gyp-linux', 'gyp-mac']