Enable bitrate probing by default in PacedSender.

BUG=crbug:425925
R=mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/33359004

Cr-Commit-Position: refs/heads/master@{#8379}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8379 4adac7df-926f-26a2-2b94-8c16560cd09d
6 files changed