Enable bitrate probing by default.

Results from the experiment were all positive.

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

Review URL: https://webrtc-codereview.appspot.com/38829004

Cr-Commit-Position: refs/heads/master@{#8231}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8231 4adac7df-926f-26a2-2b94-8c16560cd09d
3 files changed