Fix gpu_tests presubmit error.

content/test/gpu/gpu_tests/pixel.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.
 import glob
 import json
 import os
 import re
 
 from gpu_tests import cloud_storage_test_base
 from gpu_tests import pixel_expectations
 import page_sets
 
-from catapult_base import cloud_storage
+from catapult_base import cloud_storage  # pylint: disable=import-error
 from telemetry.page import page_test
 from telemetry.util import image_util
 
 
 test_data_dir = os.path.abspath(os.path.join(
     os.path.dirname(__file__), '..', '..', 'data', 'gpu'))
 
 default_reference_image_dir = os.path.join(test_data_dir, 'gpu_reference')
 
 test_harness_script = r"""
@@ skipping 158 matching lines @@
 
   def CreateStorySet(self, options):
     story_set = page_sets.PixelTestsStorySet(self.GetExpectations(),
                                              try_es3=True)
     for page in story_set:
       page.script_to_evaluate_on_commit = test_harness_script
     return story_set
 
   def _CreateExpectations(self):
     return pixel_expectations.PixelExpectations()