This is strange, the error happens when Telemetry try to do backcompat clock sync, but in this case it should be using the devtool based clock sync. The log shows that happens because Chrome revision returned by devtool is None:

INFO:root:Chrome version: None  # <--- ???
INFO:root:*************** BROWSER STANDARD OUTPUT ***************
INFO:root:Cannot get standard output on Android
INFO:root:*********** END OF BROWSER STANDARD OUTPUT ************
INFO:root:********************* BROWSER LOG *********************
INFO:root:No log file

I think this is probably a bug in devtool. The page is still running fine when this fails:

https://console.developers.google.com/m/cloudstorage/b/chrome-telemetry-output/o/profiler-file-id_13-2016-10-19_16-38-3362242.png

(https://luci-logdog.appspot.com/v/?s=chrome%2Fbb%2Fchromium.perf%2FAndroid_Nexus5_Perf__3_%2F3502%2F%2B%2Frecipes%2Fsteps%2Fpage_cycler_v2.intl_ar_fa_he%2F0%2Fstdout)

Found another instance of this in  issue 657875 

https://build.chromium.org/p/chromium.perf/builders/Mac%20HDD%20Perf%20%285%29/builds/2967/steps/service_worker.service_worker/logs/stdio

Ned, I'm not sure how I can help here. Looking at the telemetry clock sync code, I think this could only happen when devtools_clients is empty here:

https://cs.chromium.org/chromium/src/third_party/catapult/telemetry/telemetry/internal/platform/tracing_agent/chrome_tracing_agent.py?rcl=0&l=138

So I wonder how a bug in DevTools, whatever it might be, could affect this?

Oh, good catch. I forget that part. It means that chrome_tracing_devtools_manager.GetActiveDevToolsClients(self._platform_backend)) is empty & devtool client has crashed before that.

I am not sure why the log is failed to display though.

Here is what get tricky to get the log:
The page navigate 

The page crashes but Telemetry doesn't know about the crash, because Telemetry doesn't interactive with it.

We start tracing. Because we bend the tracing API to make it a platform level thing, we don't know about the crash either, all we know is there is no devtool clients available to request tracing.

Zhen: I am really swamped at this point. Can you find a way to throw ChromeCrash Exception in ChromeTracingAgent in appropriate way to show the chrome crash stack?

Current chrome crash stack is handled by inspector_backend.py. Why do we want to do it again in chrome tracing agent?

Zhen: inspector_backend only throw chrome crash stack if you invoke method calls on it. In this situation, Chrome crashes somewhere between the last call to inspector_backend  & platform.tracing_controller.Start(), hence we completely have no information about what went wrong.

That seems not Chrome tracing agent's responsibility. Chrome tracing agent has no knowledge about whether Chrome is running or not before starting tracing. If not, it will just do startup tracing. After tracing is started, Telemetry should ensure browser is running, or start the browser.

So I think shared_page_state.WillRunStory should make sure browser is up and running?

Hmhh, then it seems like a fix here could be we should add s.t in page_cycler_v2 page to ensure the browser is mostly idle after load. If the browser crashed, the logic of checking browser's idle state will report the crash.

Reassign to ksakamoto@ to add such thing to to page_cycler_v2.intl_ar_fa_he. Maybe we can use https://cs.chromium.org/chromium/src/third_party/catapult/telemetry/telemetry/internal/browser/web_contents.py?rcl=0&l=138

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/59ccf0918519486b7555d670af981eb9579532e1

commit 59ccf0918519486b7555d670af981eb9579532e1
Author: catapult-deps-roller <catapult-deps-roller@chromium.org>
Date: Mon Oct 24 19:41:59 2016

Roll src/third_party/catapult/ 4d43e1baa..dd582ea21 (3 commits).

https://chromium.googlesource.com/external/github.com/catapult-project/catapult.git/+log/4d43e1baaf06..dd582ea2140c

$ git log 4d43e1baa..dd582ea21 --date=short --no-merges --format='%ad %ae %s'
2016-10-24 jbudorick [dependency manager] Add an update script.
2016-10-24 bpastene devil: Change in type of temp dumped in device monitor to float.
2016-10-24 nednguyen Update ChromeTracingAgent exception handling

BUG=649481, 657674 

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, see:
http://www.chromium.org/developers/tree-sheriffs/sheriff-details-chromium#TOC-Failures-due-to-DEPS-rolls

CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel
TBR=catapult-sheriff@chromium.org

Review-Url: https://codereview.chromium.org/2444033002
Cr-Commit-Position: refs/heads/master@{#427120}

[modify] https://crrev.com/59ccf0918519486b7555d670af981eb9579532e1/DEPS