loading.mobile failing on 2 builders

Builders failed on: 
- Android Nexus6 WebView Perf: 
  https://build.chromium.org/p/chromium.perf/builders/Android%20Nexus6%20WebView%20Perf
- Android One Perf: 
  https://build.chromium.org/p/chromium.perf/builders/Android%20One%20Perf


Traceback (most recent call last):
  RunBenchmark at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/story_runner.py:332
    expectations=expectations, metadata=benchmark.GetMetadata())
  Run at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/story_runner.py:212
    state.TearDownState()
  traced_function at /b/swarming/w/ir/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:75
    return func(*args, **kwargs)
  TearDownState at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/page/shared_page_state.py:337
    self._StopBrowser()
  traced_function at /b/swarming/w/ir/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:75
    return func(*args, **kwargs)
  _StopBrowser at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/page/shared_page_state.py:343
    self._browser.Close()
  Close at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/browser/browser.py:278
    self._browser_backend.Close()
  traced_function at /b/swarming/w/ir/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:75
    return func(*args, **kwargs)
  Close at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/backends/chrome/android_browser_backend.py:261
    self._StopBrowser()
  traced_function at /b/swarming/w/ir/third_party/catapult/common/py_trace_event/py_trace_event/trace_event_impl/decorators.py:75
    return func(*args, **kwargs)
  _StopBrowser at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/backends/chrome/android_browser_backend.py:78
    self.platform_backend.StopApplication(self._backend_settings.package)
  StopApplication at /b/swarming/w/ir/third_party/catapult/telemetry/telemetry/internal/platform/android_platform_backend.py:371
    self._device.ForceStop(application)
  timeout_retry_wrapper at /b/swarming/w/ir/third_party/catapult/devil/devil/android/decorators.py:57
    retry_if_func=retry_if_func)
  Run at /b/swarming/w/ir/third_party/catapult/devil/devil/utils/timeout_retry.py:157
    error_log_func=error_log_func)
  JoinAll at /b/swarming/w/ir/third_party/catapult/devil/devil/utils/reraiser_thread.py:186
    self._JoinAll(watcher, timeout)
  _JoinAll at /b/swarming/w/ir/third_party/catapult/devil/devil/utils/reraiser_thread.py:158
    thread.ReraiseIfException()
  run at /b/swarming/w/ir/third_party/catapult/devil/devil/utils/reraiser_thread.py:81
    self._ret = self._func(*self._args, **self._kwargs)
  <lambda> at /b/swarming/w/ir/third_party/catapult/devil/devil/utils/timeout_retry.py:150
    child_thread = reraiser_thread.ReraiserThread(lambda: func(*args, **kwargs),
  impl at /b/swarming/w/ir/third_party/catapult/devil/devil/android/decorators.py:47
    return f(*args, **kwargs)
  ForceStop at /b/swarming/w/ir/third_party/catapult/devil/devil/android/device_utils.py:1265
    if self.GetPids(package):
  timeout_retry_wrapper at /b/swarming/w/ir/third_party/catapult/devil/devil/android/decorators.py:51
    return impl()
  impl at /b/swarming/w/ir/third_party/catapult/devil/devil/android/decorators.py:47
    return f(*args, **kwargs)
  GetPids at /b/swarming/w/ir/third_party/catapult/devil/devil/android/device_utils.py:2272
    '%s | grep -F %s' % (ps_cmd, cmd_helper.SingleQuote(process_name)))
  _RunPipedShellCommand at /b/swarming/w/ir/third_party/catapult/devil/devil/android/device_utils.py:1063
    output = self.RunShellCommand(script, **kwargs)
  timeout_retry_wrapper at /b/swarming/w/ir/third_party/catapult/devil/devil/android/decorators.py:51
    return impl()
  impl at /b/swarming/w/ir/third_party/catapult/devil/devil/android/decorators.py:47
    return f(*args, **kwargs)
  RunShellCommand at /b/swarming/w/ir/third_party/catapult/devil/devil/android/device_utils.py:1041
    output = handle_large_output(cmd, large_output)
  handle_large_output at /b/swarming/w/ir/third_party/catapult/devil/devil/android/device_utils.py:1010
    return handle_large_command(cmd)
  handle_large_command at /b/swarming/w/ir/third_party/catapult/devil/devil/android/device_utils.py:992
    return handle_check_return(cmd)
  handle_check_return at /b/swarming/w/ir/third_party/catapult/devil/devil/android/device_utils.py:983
    return run(cmd)
  run at /b/swarming/w/ir/third_party/catapult/devil/devil/android/device_utils.py:979
    return self.adb.Shell(cmd)
  Shell at /b/swarming/w/ir/third_party/catapult/devil/devil/android/sdk/adb_wrapper.py:505
    output = self._RunDeviceAdbCmd(args, timeout, retries, check_error=False)
  _RunDeviceAdbCmd at /b/swarming/w/ir/third_party/catapult/devil/devil/android/sdk/adb_wrapper.py:301
    check_error=check_error)
  timeout_retry_wrapper at /b/swarming/w/ir/third_party/catapult/devil/devil/android/decorators.py:51
    return impl()
  impl at /b/swarming/w/ir/third_party/catapult/devil/devil/android/decorators.py:47
    return f(*args, **kwargs)
  _RunAdbCmd at /b/swarming/w/ir/third_party/catapult/devil/devil/android/sdk/adb_wrapper.py:278
    raise device_errors.DeviceUnreachableError(device_serial)
DeviceUnreachableError: ZX1G22L2B7

Locals:
  args             : ['shell', '( ps | grep -F org.chromium.webview_shell; echo "PIPESTATUS: ${PIPESTATUS[@]}" );echo %$?']
  check_error      : False
  cls              : <class 'devil.android.sdk.adb_wrapper.AdbWrapper'>
  cpu_affinity     : None
  device_serial    : 'ZX1G22L2B7'
  device_waiting_m : None
  not_found_m      : <_sre.SRE_Match object at 0x7f6d9f2165d0>
  output           : "error: device 'ZX1G22L2B7' not found\n"
  retries          : 2
  status           : 255
  timeout          : 30