Fix follow-up in webrtc/test/field_trial.cc.
Fix follow-up in webrtc/test/field_trial.cc.

BUG=webrtc:4820
R=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1215713019

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9563}

TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc