Add a presubmit script and pylintrc for content/test/gpu

content/test/gpu/run_unittests.py

 #!/usr/bin/env python
 # Copyright 2015 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.
 
 """This script runs unit tests of the code in the gpu_tests/ directory.
 
 This script DOES NOT run tests. run_gpu_test does that.
 """
 
-import os
-import subprocess
 import sys
 
 from gpu_tests import path_util
 import gpu_project_config
 
 path_util.AddDirToPathIfNeeded(path_util.GetChromiumSrcDir(), 'tools',
                                'telemetry')
 
 from telemetry.testing import unittest_runner
 
 def main():
   return unittest_runner.Run(gpu_project_config.CONFIG, no_browser=True)
 
 if __name__ == '__main__':
   sys.exit(main())