Number of failures seen on recent builds since 779: 12111---

Example recent build:
https://luci-milo.appspot.com/buildbot/chromium.perf/Win%207%20ATI%20GPU%20Perf/779

The error happens while trying to navigate to an item, waiting for an element to appear:

  File "c:\b\s\w\ir\tools\perf\page_sets\system_health\browsing_stories.py", line 38, in _NavigateToItem
    action_runner.WaitForElement(element_function=item_selector)
  File "c:\b\s\w\ir\third_party\catapult\common\py_trace_event\py_trace_event\trace_event_impl\decorators.py", line 75, in traced_function
    return func(*args, **kwargs)
  File "c:\b\s\w\ir\third_party\catapult\telemetry\telemetry\internal\actions\action_runner.py", line 280, in WaitForElement
    timeout_in_seconds=timeout_in_seconds))

And a second timeout exception is raised while trying to stop tracing and gather a trace:

ChromeTracingStoppedError: Exceptions raised when trying to stop Chrome devtool tracing:
Error when trying to stop Chrome tracing on devtools at port 63794:
Traceback (most recent call last):
  File "c:\b\s\w\ir\third_party\catapult\telemetry\telemetry\internal\platform\tracing_agent\chrome_tracing_agent.py", line 214, in StopAgentTracing
    client.StopChromeTracing()
  File "c:\b\s\w\ir\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\devtools_client_backend.py", line 360, in StopChromeTracing
    backend_id=backend.id)
  File "c:\b\s\w\ir\third_party\catapult\common\py_trace_event\py_trace_event\trace_event_impl\decorators.py", line 75, in traced_function
    return func(*args, **kwargs)
  File "c:\b\s\w\ir\third_party\catapult\telemetry\telemetry\internal\backends\chrome_inspector\inspector_backend.py", line 243, in EvaluateJavaScript
    return self._EvaluateJavaScript(expression, context_id, timeout)
[...]
  File "c:\b\s\w\ir\third_party\catapult\telemetry\third_party\websocket-client\websocket\_socket.py", line 83, in recv
    raise WebSocketTimeoutException(message)
TimeoutException: 

Furthermore, there is a timeout exception when trying to take a screenshot:
WARNING:root:Exception when trying to capture screenshot: TimeoutException('',)

Full log:
https://luci-logdog.appspot.com/v/?s=chrome%2Fbb%2Fchromium.perf%2FWin_7_ATI_GPU_Perf%2F779%2F%2B%2Frecipes%2Fsteps%2Fsystem_health.memory_desktop_on_ATI_GPU_on_Windows_on_Windows-2008ServerR2-SP1%2F0%2Fstdout

First failure was spotted at:
https://luci-milo.appspot.com/buildbot/chromium.perf/Win%207%20ATI%20GPU%20Perf/775

With cl range:
http://test-results.appspot.com/revision_range?start=474275&end=474398