More, potentially relevant context:

[1069/1069] telemetry.web_perf.timeline_based_page_test_unittest.TimelineBasedPageTestTest.testTBM2ForSmoke passed 9.0650s:
  Chrome build location for win_AMD64 not found. Browser will be run without Flash.
  Trace config file string: {"trace_config": {"included_categories": ["toplevel", "trace_event_overhead", "benchmark", "blink.console", "webkit.console"], "record_mode": "record-as-much-as-possible"}}
  Requested remote debugging port: 0
  Starting Chrome ['../../out\\Release_x64\\chrome.exe', '--enable-net-benchmarking', '--metrics-recording-only', '--no-default-browser-check', '--no-first-run', '--enable-gpu-benchmarking', '--disable-background-networking', '--disable-component-extensions-with-background-pages', '--disable-default-apps', '--remote-debugging-port=0', '--enable-crash-reporter-for-testing', '--window-size=1280,1024', '--user-data-dir=e:\\b\\swarm_slave\\w\\itivfxdx\\tmpaa3yly', '--trace-config-file=e:\\b\\swarm_slave\\w\\itivfxdx\\tmp3ogqnj\\chrome-trace-config.json', 'about:blank']
  Discovered ephemeral port 63618
  OS: win win7
  GPU device 0: VENDOR = 0x15ad, DEVICE = 0x405
  GPU Attributes:
    adapter_luid        : 0.0
    amd_switchable      : False
    basic_info_state    : 1
    context_info_state  : 3
    direct_rendering    : True
    driver_date         : 11-11-2013
    driver_vendor       : VMware, Inc.
    driver_version      : 7.14.1.2032
    dx_diagnostics_info_state: 3
    gl_extensions       : 
    gl_renderer         : 
    gl_reset_notification_strategy: 0
    gl_vendor           : 
    gl_version          : 
    gl_ws_extensions    : 
    gl_ws_vendor        : 
    gl_ws_version       : 
    in_process_gpu      : True
    initialization_time : 0.0
    jpeg_decode_accelerator_supported: False
    lenovo_dcute        : False
    max_msaa_samples    : 
    optimus             : False
    pixel_shader_version: 
    process_crash_count : 0
    sandboxed           : False
    software_rendering  : False
    vertex_shader_version: 
    video_decode_accelerator_flags: 0
  Feature Status:
    2d_canvas           : unavailable_software
    flash_3d            : unavailable_software
    flash_stage3d       : unavailable_software
    flash_stage3d_baseline: unavailable_software
    gpu_compositing     : unavailable_software
    multiple_raster_threads: unavailable_off
    native_gpu_memory_buffers: disabled_software
    rasterization       : unavailable_software
    video_decode        : unavailable_software
    video_encode        : unavailable_software
    vpx_decode          : unavailable_software
    webgl               : unavailable_off
  Driver Bug Workarounds:
    clear_uniforms_before_first_program_use
    disable_direct_composition
    disable_discard_framebuffer
    disable_dxgi_zero_copy_video
    disable_framebuffer_cmaa
    exit_on_context_lost
    scalarize_vec_and_mat_constructor_args
  PageCacheTemperature: any
  Error when deleting e:\b\swarm_slave\w\itivfxdx\tmp0ffvg1, will try again at exit.
  Traceback (most recent call last):
    File "e:\b\swarm_slave\w\irl4nbto\third_party\catapult\telemetry\telemetry\internal\platform\tracing_controller_backend.py", line 271, in CollectAgentTraceData
      os.remove(self._trace_log)
  WindowsError: [Error 32] The process cannot access the file because it is being used by another process: 'e:\\b\\swarm_slave\\w\\itivfxdx\\tmp0ffvg1'
  Trace (TraceDataPart("traceEvents")) of size 665723 bytes saved.
  Trace (TraceDataPart("tabIds")) of size 40 bytes saved.
  Trace (TraceDataPart("telemetry")) of size 1225 bytes saved.
  Successfully shut down browser cooperatively

Retrying failed tests (attempt #1 of 3)...

[1/1] telemetry.internal.results.csv_pivot_table_output_formatter_unittest.CsvPivotTableOutputFormatterTest.testMultiplePagesAndValues failed unexpectedly 0.0000s:
  No traces to convert to html.
  View generated trace files online at https://cloud_storage_url/foo for page unknown
  Traceback (most recent call last):
    File "e:\b\swarm_slave\w\irl4nbto\third_party\catapult\telemetry\third_party\mock\mock.py", line 1201, in patched
      return func(*args, **keywargs)
    File "e:\b\swarm_slave\w\irl4nbto\third_party\catapult\telemetry\telemetry\internal\results\csv_pivot_table_output_formatter_unittest.py", line 110, in testMultiplePagesAndValues
      'https://cloud_storage_url/foo', '', '1'])
  AssertionError: Lists differ: ['story_set', 'http://www.bar.... != ['story_set', 'http://www.bar....
  
  First differing element 5:
  0
  1
  
    ['story_set',
     'http://www.bar.com/',
     'trace',
     'https://cloud_storage_url/foo',
     '',
  -  '0']
  ?   ^
  
  +  '1']
  ?   ^
  

Should be fixed once https://codereview.chromium.org/2293973003/ lands