Example failures:

https://build.chromium.org/p/chromium.perf/builders/Win%20Zenbook%20Perf%20%282%29/builds/2229/steps/smoothness.tough_webgl_cases.reference/logs/stdio/text

[ RUN      ] http://kenrussell.github.io/webgl-animometer/Animometer/tests/3d/webgl.html
(INFO) 2016-05-18 04:03:46,548 cache_temperature.EnsurePageCacheTemperature:29  PageCacheTemperature: any
(INFO) 2016-05-18 04:03:47,221 chrome_tracing_agent._CreateTraceConfigFile:243  Trace config file string: {"trace_config":{"included_categories": ["webkit.console", "benchmark", "blink.console", "trace_event_overhead"], "record_mode": "record-as-much-as-possible"}}
(INFO) 2016-05-18 04:03:47,301 tracing_backend.StartTracing:124  Start Tracing Request: {'params': {'transferMode': 'ReturnAsStream', 'options': 'record-as-much-as-possible', 'categories': 'webkit.console,benchmark,blink.console,trace_event_overhead'}, 'method': 'Tracing.start'}
(WARNING) 2016-05-18 04:05:47,371 shared_page_state._TryCaptureScreenShot:153  Exception when trying to capture screenshot: TimeoutException('',)
Traceback (most recent call last):
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\story_runner.py", line 84, in _RunStoryAndProcessErrorIfNeeded
    state.RunStory(results)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\page\shared_page_state.py", line 330, in RunStory
    self._current_page.Run(self)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\page\__init__.py", line 95, in Run
    shared_state.page_test.RunNavigateSteps(self, current_tab)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\page\legacy_page_test.py", line 191, in RunNavigateSteps
    page.RunNavigateSteps(action_runner)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\tools\perf\page_sets\tough_webgl_cases.py", line 29, in RunNavigateSteps
    super(ToughWebglCasesPage, self).RunNavigateSteps(action_runner)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\page\__init__.py", line 104, in RunNavigateSteps
    url, script_to_evaluate_on_commit=self.script_to_evaluate_on_commit)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\actions\action_runner.py", line 121, in Navigate
    timeout_in_seconds=timeout_in_seconds))
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\actions\action_runner.py", line 44, in _RunAction
    action.RunAction(self._tab)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\actions\navigate.py", line 23, in RunAction
    self._timeout_in_seconds)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\browser\web_contents.py", line 252, in Navigate
    self._inspector_backend.Navigate(url, script_to_evaluate_on_commit, timeout)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\inspector_backend.py", line 35, in inner
    inspector_backend._ConvertExceptionFromInspectorWebsocket(e)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\inspector_backend.py", line 32, in inner
    return func(inspector_backend, *args, **kwargs)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\inspector_backend.py", line 167, in Navigate
    self._page.Navigate(url, script_to_evaluate_on_commit, timeout)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\inspector_page.py", line 112, in Navigate
    res = self._inspector_websocket.SyncRequest(request, timeout)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\inspector_websocket.py", line 110, in SyncRequest
    res = self._Receive(timeout)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\inspector_websocket.py", line 149, in _Receive
    data = self._socket.recv()
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\third_party\websocket-client\websocket.py", line 596, in recv
    opcode, data = self.recv_data()
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\third_party\websocket-client\websocket.py", line 606, in recv_data
    frame = self.recv_frame()
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\third_party\websocket-client\websocket.py", line 637, in recv_frame
    self._frame_header = self._recv_strict(2)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\third_party\websocket-client\websocket.py", line 746, in _recv_strict
    bytes = self._recv(shortage)
  File "C:\b\build\slave\Win_Zenbook_Perf__2_\build\src\third_party\catapult\telemetry\third_party\websocket-client\websocket.py", line 732, in _recv
    raise WebSocketTimeoutException(e.message)
TimeoutException: 

I'll disable this benchmark on the reference builds for now.