Optimize variation field trial evaluation.

Optimize variation field trial evaluation.

For studies where there is a single group with 100%
probability, avoid doing more expensive random entropy
computation, since it's not needed to know the final
result.

BUG=460481
Committed: https://crrev.com/30ac09133a00579c37010f9e0a23434287a736f8
Cr-Commit-Position: refs/heads/master@{#317378}

[Alexei Svitkine (slow), 2015-02-20 16:33:28]

Patchset #1 (id:1) has been deleted

[Alexei Svitkine (slow), 2015-02-20 16:34:31]

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

[jwd, 2015-02-20 18:56:31]

lgtm

https://codereview.chromium.org/947493002/diff/20001/components/variations/pr...
File components/variations/processed_study.cc (right):

https://codereview.chromium.org/947493002/diff/20001/components/variations/pr...
components/variations/processed_study.cc:60: if (divisor != 0)
Clever!
If you can think of a succinct comment for it though, that would be great.

[Alexei Svitkine (slow), 2015-02-20 19:01:10]

New patchsets have been uploaded after l-g-t-m from jwd@chromium.org

[Alexei Svitkine (slow), 2015-02-20 19:03:07]

https://codereview.chromium.org/947493002/diff/20001/components/variations/pr...
File components/variations/processed_study.cc (right):

https://codereview.chromium.org/947493002/diff/20001/components/variations/pr...
components/variations/processed_study.cc:60: if (divisor != 0)
On 2015/02/20 18:56:31, Jesse Doherty wrote:
> Clever!
> If you can think of a succinct comment for it though, that would be great.

Done.

[Alexei Svitkine (slow), 2015-02-20 19:03:10]

The CQ bit was checked by asvitkine@chromium.org

[commit-bot: I haz the power, 2015-02-20 19:03:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/947493002/40001

[Alexei Svitkine (slow), 2015-02-20 19:41:38]

The CQ bit was checked by asvitkine@chromium.org

[Alexei Svitkine (slow), 2015-02-20 19:41:52]

Patchset #3 (id:60001) has been deleted

[commit-bot: I haz the power, 2015-02-20 19:42:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/947493002/40001

[commit-bot: I haz the power, 2015-02-20 19:50:20]

Committed patchset #2 (id:40001)

[commit-bot: I haz the power, 2015-02-20 19:51:04]

Patchset 2 (id:??) landed as
https://crrev.com/30ac09133a00579c37010f9e0a23434287a736f8
Cr-Commit-Position: refs/heads/master@{#317378}