Don't use result of "field_trial::FindFullName" as string reference.

Don't use result of "field_trial::FindFullName" as string reference.

"field_trial::FindFullName" can return "std::string()" which should not
be referenced by the caller.

Committed: https://crrev.com/bd3842808996dbb85007242214352f1e6ebd3d17
Cr-Commit-Position: refs/heads/master@{#9594}

[joachim, 2015-07-16 10:03:14]

jbauch@webrtc.org changed reviewers:
+ pthatcher@webrtc.org

[joachim, 2015-07-16 10:03:15]

ptal, this addresses the potential problem you found in
https://codereview.webrtc.org/1241973002/

[pthatcher1, 2015-07-16 10:06:32]

lgtm

[joachim, 2015-07-16 10:07:04]

The CQ bit was checked by jbauch@webrtc.org

[commit-bot: I haz the power, 2015-07-16 10:07:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1238943003/1

[commit-bot: I haz the power, 2015-07-16 11:06:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-16 11:06:12]

Patchset 1 (id:??) landed as
https://crrev.com/bd3842808996dbb85007242214352f1e6ebd3d17
Cr-Commit-Position: refs/heads/master@{#9594}