Added missing import.

content/test/gpu/gpu_tests/context_lost.py

 # Copyright (c) 2013 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 os
 
 from telemetry import test as test_module
+from telemetry.core import exceptions
 from telemetry.core import util
 from telemetry.page import page_set
 from telemetry.page import page_test
 
 data_path = os.path.join(
     util.GetChromiumSrcDir(), 'content', 'test', 'data', 'gpu')
 
 wait_timeout = 20  # seconds
 
 harness_script = r"""
@@ skipping 113 matching lines @@
           'navigate_steps': [
             { 'action': 'navigate' },
             { 'action': 'wait',
               'javascript': 'window.domAutomationController._finished' }
           ],
           'kill_gpu_process': False
         },
       ]
     }
     return page_set.PageSet.FromDict(page_set_dict, data_path)