Modify default field trial implementation to allow
WebRTC client to turn on feature code.

R=andresp@webrtc.org, henrika@webrtc.org, mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/39729004

Cr-Commit-Position: refs/heads/master@{#8301}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8301 4adac7df-926f-26a2-2b94-8c16560cd09d
4 files changed