Resolve conflict in chrome://flags and field trial config.

Resolve conflict in chrome://flags and field trial config.

Chrome crashed when the same finch field trial is specified in
chrome://flags and in field trial config. The trial variation parameters
selected in chrome://flags are registered first. Registering overrides
from field trial config happens later (and may cause a DCHECK failure).

This CL skips field trials from the trial config that have been
registered before (from chrome://flags).

BUG=636765
Committed: https://crrev.com/25e794db58321015633eb287553b8a529eb8e309
Cr-Commit-Position: refs/heads/master@{#411558}

[jkrcal, 2016-08-11 09:52:18]

jkrcal@chromium.org changed reviewers:
+ asvitkine@chromium.org

[jkrcal, 2016-08-11 09:52:19]

Alexei, PTAL!

Context: yesterday, a trial config for NTPSnippets landed, so the bug appeared
today for me because I override the same trial from chrome://flags.

[jkrcal, 2016-08-11 09:59:35]

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

[commit-bot: I haz the power, 2016-08-11 09:59:41]

Dry run: 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, 2016-08-11 10:40:10]

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

[commit-bot: I haz the power, 2016-08-11 10:40:10]

Dry run: This issue passed the CQ dry run.

[Alexei Svitkine (slow), 2016-08-11 15:51:31]

Would this only be the case for Chromium builds where user explicitly set
something in chrome://flags? (Since Google Chrome builds don't use the testing
config, iirc.)

Could it ever happen if the user never set something in chrome://flags? (i.e. I
want to make sure field trial testing config should be applied if specified
without any specific user behavior)

LGTM if the answers to the above questions are yes and no. Otherwise, let's
discuss more.

[jkrcal, 2016-08-12 05:32:18]

On 2016/08/11 15:51:31, Alexei Svitkine (very slow) wrote:
> Would this only be the case for Chromium builds where user explicitly set
> something in chrome://flags? (Since Google Chrome builds don't use the testing
> config, iirc.)
> 
> Could it ever happen if the user never set something in chrome://flags? (i.e.
I
> want to make sure field trial testing config should be applied if specified
> without any specific user behavior)
> 
> LGTM if the answers to the above questions are yes and no. Otherwise, let's
> discuss more.

Indeed, the answers are yes and no. Thanks!

[jkrcal, 2016-08-12 05:32:26]

The CQ bit was checked by jkrcal@chromium.org

[commit-bot: I haz the power, 2016-08-12 05:32:38]

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, 2016-08-12 05:36:34]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-08-12 05:37:55]

Description was changed from

==========
Resolve conflict in chrome://flags and field trial config.

Chrome crashed when the same finch field trial is specified in
chrome://flags and in field trial config. The trial variation parameters
selected in chrome://flags are registered first. Registering overrides
from field trial config happens later (and may cause a DCHECK failure).

This CL skips field trials from the trial config that have been
registered before (from chrome://flags).

BUG=636765
==========

to

==========
Resolve conflict in chrome://flags and field trial config.

Chrome crashed when the same finch field trial is specified in
chrome://flags and in field trial config. The trial variation parameters
selected in chrome://flags are registered first. Registering overrides
from field trial config happens later (and may cause a DCHECK failure).

This CL skips field trials from the trial config that have been
registered before (from chrome://flags).

BUG=636765

Committed: https://crrev.com/25e794db58321015633eb287553b8a529eb8e309
Cr-Commit-Position: refs/heads/master@{#411558}
==========

[commit-bot: I haz the power, 2016-08-12 05:37:56]

Patchset 1 (id:??) landed as
https://crrev.com/25e794db58321015633eb287553b8a529eb8e309
Cr-Commit-Position: refs/heads/master@{#411558}