tracing: Bail out early in tracing tests when tracing is already enabled

tracing: Bail out early in tracing tests when tracing is already enabled

A bunch of tracing browsertests have recently become flaky.
I strongly suspect this is because some other test leaves the
startup tracing file (/data/local/chrome-trace-config.json)
around. On Android the presence of that file is enough to
initialize the tracing machinery and interfere with tests.
Bail out early explicitly in that case.

BUG=657628, 656729
Committed: https://crrev.com/ea26a4f05c216cd7dd7d76ea19fc46665c300baa
Cr-Commit-Position: refs/heads/master@{#429593}

[Primiano Tucci (use gerrit), 2016-11-03 14:26:31]

The CQ bit was checked by primiano@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-11-03 14:26:50]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Primiano Tucci (use gerrit), 2016-11-03 14:30:17]

primiano@chromium.org changed reviewers:
+ ssid@chromium.org

[Primiano Tucci (use gerrit), 2016-11-03 14:30:17]

PTAL, small check

[ssid, 2016-11-03 14:53:13]

lgtm
Yes this would confirm your theory in issue 656729.
But, I don't see any browsertest that creates the chrome-trace-config.json file.

[commit-bot: I haz the power, 2016-11-03 14:59:22]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2016-11-03 14:59:23]

Dry run: This issue passed the CQ dry run.

[Primiano Tucci (use gerrit), 2016-11-03 15:16:43]

> But, I don't see any browsertest that creates the chrome-trace-config.json
file.

The telemetry tests :)
These days I believe that swarming runs different tests on the same device, not
necessarily only browsertests.

[Primiano Tucci (use gerrit), 2016-11-03 15:16:46]

The CQ bit was checked by primiano@chromium.org

[commit-bot: I haz the power, 2016-11-03 15:17:10]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-11-03 15:22:30]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-11-03 15:40:57]

Description was changed from

==========
tracing: Bail out early in tracing tests when tracing is already enabled

A bunch of tracing browsertests have recently become flaky.
I strongly suspect this is because some other test leaves the
startup tracing file (/data/local/chrome-trace-config.json)
around. On Android the presence of that file is enough to
initialize the tracing machinery and interfere with tests.
Bail out early explicitly in that case.

BUG=657628, 656729
==========

to

==========
tracing: Bail out early in tracing tests when tracing is already enabled

A bunch of tracing browsertests have recently become flaky.
I strongly suspect this is because some other test leaves the
startup tracing file (/data/local/chrome-trace-config.json)
around. On Android the presence of that file is enough to
initialize the tracing machinery and interfere with tests.
Bail out early explicitly in that case.

BUG=657628, 656729

Committed: https://crrev.com/ea26a4f05c216cd7dd7d76ea19fc46665c300baa
Cr-Commit-Position: refs/heads/master@{#429593}
==========

[commit-bot: I haz the power, 2016-11-03 15:40:57]

Patchset 1 (id:??) landed as
https://crrev.com/ea26a4f05c216cd7dd7d76ea19fc46665c300baa
Cr-Commit-Position: refs/heads/master@{#429593}