Wire up preferred/nominal_bitrate to stats.

Also adds a test that shows that actual_enc_bitrate was not summed
correctly plus fixing it.

Additionally reducing locking when grabbing stats.

BUG=1778
R=stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/34319004

Cr-Commit-Position: refs/heads/master@{#8464}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8464 4adac7df-926f-26a2-2b94-8c16560cd09d
2 files changed