Add pylint presubmit check to src/testing

testing/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 testing.
+
+See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts for
+details on the presubmit API built into gcl.
+"""
+
+
+def CommonChecks(input_api, output_api):
+  output = []
+  blacklist = [r'gmock.*', r'gtest.*']
+  output.extend(input_api.canned_checks.RunPylint(
+      input_api, output_api, black_list=blacklist))
+  return output
+
+
+def CheckChangeOnUpload(input_api, output_api):
+  return CommonChecks(input_api, output_api)
+
+
+def CheckChangeOnCommit(input_api, output_api):
+  return CommonChecks(input_api, output_api)