Add ability to control peer connection constraints for the loopback test.

R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/11419005

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5879 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed