This could be the result of an upstream failure, but if that's the case, it should be caught and reported differently.

https://uberchromegw.corp.google.com/i/chromeos/builders/buddy-release/builds/210/steps/AUTest%20%5Bau%5D/logs/stdio

see this snippet:

21:09:46: INFO: RunCommand: /b/cbuild/internal_master/chromite/third_party/swarming.client/swarming.py run --swarming chromeos-proxy.appspot.com --task-summary-json /tmp/cbuildbot-tmp4wEuHh/tmpCx9C4x/temp_summary.json --raw-cmd --task-name buddy-release/R54-8589.0.0-au --dimension os Ubuntu-14.04 --dimension pool default --print-status-updates --timeout 14400 --io-timeout 14400 --hard-timeout 14400 --expiration 1200 -- /usr/local/autotest/site_utils/run_suite.py --build buddy-release/R54-8589.0.0 --board buddy --suite_name au --pool bvt --num 2 --file_bugs True --priority CQ --timeout_mins 180 --retry True --max_retries 10 --minimum_duts 4 --suite_min_duts 6 --offload_failures_only False -m 69630926
21:10:08: WARNING: Exception is not retriable return code: 3; command: /b/cbuild/internal_master/chromite/third_party/swarming.client/swarming.py run --swarming chromeos-proxy.appspot.com --task-summary-json /tmp/cbuildbot-tmp4wEuHh/tmpCx9C4x/temp_summary.json --raw-cmd --task-name buddy-release/R54-8589.0.0-au --dimension os Ubuntu-14.04 --dimension pool default --print-status-updates --timeout 14400 --io-timeout 14400 --hard-timeout 14400 --expiration 1200 -- /usr/local/autotest/site_utils/run_suite.py --build buddy-release/R54-8589.0.0 --board buddy --suite_name au --pool bvt --num 2 --file_bugs True --priority CQ --timeout_mins 180 --retry True --max_retries 10 --minimum_duts 4 --suite_min_duts 6 --offload_failures_only False -m 69630926
Priority was reset to 100
Triggered task: buddy-release/R54-8589.0.0-au
chromeos-server22-30: 300590825a43f110 3
  Autotest instance: cautotest
  07-14-2016 [21:09:43] Created suite job: http://cautotest.corp.google.com/afe/#tab_id=view_job&object_id=69630926
  @@@STEP_LINK@Link to suite@http://cautotest.corp.google.com/afe/#tab_id=view_job&object_id=69630926@@@
  Unhandled run_suite exception: 'NoneType' object has no attribute 'download_start_time'
  Traceback (most recent call last):
    File "/usr/local/autotest/site_utils/run_suite.py", line 1705, in main
      (code, output_dict) = main_without_exception_handling(options)
    File "/usr/local/autotest/site_utils/run_suite.py", line 1629, in main_without_exception_handling
      output_dict = collector.get_results_dict()
    File "/usr/local/autotest/site_utils/run_suite.py", line 1371, in get_results_dict
      'download_start' : str(self.timings.download_start_time),
  AttributeError: 'NoneType' object has no attribute 'download_start_time'
  Will return from run_suite with status: INFRA_FAILURE