Introduce a new FieldTrialList::IsTrialActive() API.

Introduce a new FieldTrialList::IsTrialActive() API.

This removes a bunch of less-efficient helper functions
scattered throughout code (mostly unit tests, but also
some production code) that queried the same info.

Also renames some params from |name| to |trial_name|
for consistency.

BUG=526169
Committed: https://crrev.com/11f882b405f348be9a286164f14205f0184ff474
Cr-Commit-Position: refs/heads/master@{#350585}

[Alexei Svitkine (slow), 2015-09-23 17:30:47]

Patchset #1 (id:1) has been deleted

[Alexei Svitkine (slow), 2015-09-23 17:33:24]

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

[Ilya Sherman, 2015-09-23 23:21:28]

LGTM.  Thanks for the cleanup =)

https://codereview.chromium.org/1366673002/diff/20001/base/metrics/field_tria...
File base/metrics/field_trial.cc (right):

https://codereview.chromium.org/1366673002/diff/20001/base/metrics/field_tria...
base/metrics/field_trial.cc:357: FieldTrial* FieldTrialList::Find(const
std::string& trial_name) {
nit: It's weird to change these without also changing the header.  I'm fine with
either name, but let's make the two files consistent.

[Alexei Svitkine (slow), 2015-09-24 15:29:51]

https://codereview.chromium.org/1366673002/diff/20001/base/metrics/field_tria...
File base/metrics/field_trial.cc (right):

https://codereview.chromium.org/1366673002/diff/20001/base/metrics/field_tria...
base/metrics/field_trial.cc:357: FieldTrial* FieldTrialList::Find(const
std::string& trial_name) {
On 2015/09/23 23:21:28, Ilya Sherman wrote:
> nit: It's weird to change these without also changing the header.  I'm fine
with
> either name, but let's make the two files consistent.

Oops, the header changes got lost when I split this off from the other CL.
Re-added them.

[Alexei Svitkine (slow), 2015-09-24 15:30:02]

The CQ bit was checked by asvitkine@chromium.org

[Alexei Svitkine (slow), 2015-09-24 15:30:02]

The patchset sent to the CQ was uploaded after l-g-t-m from
isherman@chromium.org
Link to the patchset: https://codereview.chromium.org/1366673002/#ps40001
(title: "Address nit.")

[commit-bot: I haz the power, 2015-09-24 15:30:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1366673002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1366673002/40001

[commit-bot: I haz the power, 2015-09-24 16:57:53]

Committed patchset #2 (id:40001)

[commit-bot: I haz the power, 2015-09-24 16:58:54]

Patchset 2 (id:??) landed as
https://crrev.com/11f882b405f348be9a286164f14205f0184ff474
Cr-Commit-Position: refs/heads/master@{#350585}